# Troubleshooting client devices
<a name="troubleshooting-client-devices"></a>

Use the troubleshooting information and solutions in this section to help resolve issues with Greengrass client devices and client device components.

**Topics**
+ [Greengrass discovery issues](#greengrass-discovery-issues)
+ [MQTT connection issues](#mqtt-connection-issues)

## Greengrass discovery issues
<a name="greengrass-discovery-issues"></a>

Use the following information to troubleshoot issues with Greengrass discovery. These issues can occur when client devices use the [Greengrass discovery API](greengrass-discover-api.md) to identify a Greengrass core device to which they can connect.

**Topics**
+ [Greengrass discovery issues (HTTP API)](#greengrass-discovery-http-issues)
+ [Greengrass discovery issues (AWS IoT Device SDK v2 for Python)](#greengrass-discovery-python-issues)
+ [Greengrass discovery issues (AWS IoT Device SDK v2 for C\+\+)](#greengrass-discovery-cpp-issues)
+ [Greengrass discovery issues (AWS IoT Device SDK v2 for JavaScript)](#greengrass-discovery-javascript-issues)
+ [Greengrass discovery issues (AWS IoT Device SDK v2 for Java)](#greengrass-discovery-java-issues)

### Greengrass discovery issues (HTTP API)
<a name="greengrass-discovery-http-issues"></a>

Use the following information to troubleshoot issues with Greengrass discovery. You might see these errors if you [test the discovery API with cURL](greengrass-discover-api.md#greengrass-discover-test-request).

**Topics**
+ [curl: (52) Empty reply from server](#greengrass-discovery-http-issue-no-response)
+ [HTTP 403: {"message":null,"traceId":"a1b2c3d4-5678-90ab-cdef-11111EXAMPLE"}](#greengrass-discovery-http-issue-forbidden)
+ [HTTP 404: {"errorMessage":"The thing provided for discovery was not found"}](#greengrass-discovery-http-issue-not-found)

#### curl: (52) Empty reply from server
<a name="greengrass-discovery-http-issue-no-response"></a>

<a name="troubleshooting-greengrass-discovery-no-response-issue"></a>You might see this error if you specify an inactive AWS IoT certificate in the request.

<a name="troubleshooting-greengrass-discovery-no-response-solution"></a>Check that the client device has an attached certificate, and that the certificate is active. For more information, see [Attach a thing or policy to a client certificate](https://docs.aws.amazon.com/iot/latest/developerguide/attach-to-cert.html) and [Activate or deactivate a client certificate](https://docs.aws.amazon.com/iot/latest/developerguide/activate-or-deactivate-device-cert.html) in the *AWS IoT Core Developer Guide*.

#### HTTP 403: {"message":null,"traceId":"a1b2c3d4-5678-90ab-cdef-11111EXAMPLE"}
<a name="greengrass-discovery-http-issue-forbidden"></a>

<a name="troubleshooting-greengrass-discovery-forbidden-issue"></a>You might see this error if the client device doesn't have permission to call `greengrass:Discover` for itself.

<a name="troubleshooting-greengrass-discovery-forbidden-solution"></a>Check that the client device's certificate has a policy that allows `greengrass:Discover`. You can't use [thing policy variables](https://docs.aws.amazon.com/iot/latest/developerguide/thing-policy-variables.html) (`iot:Connection.Thing.{{*}}`) in the `Resource` section for this permission. For more information, see [Discovery authentication and authorization](greengrass-discover-api.md#greengrass-discover-auth).

#### HTTP 404: {"errorMessage":"The thing provided for discovery was not found"}
<a name="greengrass-discovery-http-issue-not-found"></a>

<a name="troubleshooting-greengrass-discovery-not-found-issue"></a>You might see this error in the following cases:<a name="troubleshooting-greengrass-discovery-not-found-issue-list"></a>
+ The client device isn't associated to any Greengrass core devices or AWS IoT Greengrass V1 groups.
+ None of the client device's associated Greengrass core devices or AWS IoT Greengrass V1 groups have an MQTT broker endpoint.
+ None of the client device's associated Greengrass core devices run the [client device auth component](client-device-auth-component.md).

<a name="troubleshooting-greengrass-discovery-not-found-solution"></a>Check that the client device is associated to the core device to which you want it to connect. Then, check that the core device runs the [client device auth component](client-device-auth-component.md) and has at least one MQTT broker endpoint. For more information, see the following:<a name="troubleshooting-greengrass-discovery-not-found-solution-links"></a>
+ [Associate client devices](associate-client-devices.md)
+ [Manage core device endpoints](manage-core-device-endpoints.md)
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)

### Greengrass discovery issues (AWS IoT Device SDK v2 for Python)
<a name="greengrass-discovery-python-issues"></a>

Use the following information to troubleshoot issues with Greengrass discovery in the [AWS IoT Device SDK v2 for Python](https://github.com/aws/aws-iot-device-sdk-python-v2).

**Topics**
+ [awscrt.exceptions.AwsCrtError: AWS\_ERROR\_HTTP\_CONNECTION\_CLOSED: The connection has closed or is closing.](#greengrass-discovery-python-issue-no-response)
+ [awsiot.greengrass\_discovery.DiscoveryException: ('Error during discover call: response\_code=403', 403)](#greengrass-discovery-python-issue-forbidden)
+ [awsiot.greengrass\_discovery.DiscoveryException: ('Error during discover call: response\_code=404', 404)](#greengrass-discovery-python-issue-not-found)

#### awscrt.exceptions.AwsCrtError: AWS\_ERROR\_HTTP\_CONNECTION\_CLOSED: The connection has closed or is closing.
<a name="greengrass-discovery-python-issue-no-response"></a>

<a name="troubleshooting-greengrass-discovery-no-response-issue"></a>You might see this error if you specify an inactive AWS IoT certificate in the request.

<a name="troubleshooting-greengrass-discovery-no-response-solution"></a>Check that the client device has an attached certificate, and that the certificate is active. For more information, see [Attach a thing or policy to a client certificate](https://docs.aws.amazon.com/iot/latest/developerguide/attach-to-cert.html) and [Activate or deactivate a client certificate](https://docs.aws.amazon.com/iot/latest/developerguide/activate-or-deactivate-device-cert.html) in the *AWS IoT Core Developer Guide*.

#### awsiot.greengrass\_discovery.DiscoveryException: ('Error during discover call: response\_code=403', 403)
<a name="greengrass-discovery-python-issue-forbidden"></a>

<a name="troubleshooting-greengrass-discovery-forbidden-issue"></a>You might see this error if the client device doesn't have permission to call `greengrass:Discover` for itself.

<a name="troubleshooting-greengrass-discovery-forbidden-solution"></a>Check that the client device's certificate has a policy that allows `greengrass:Discover`. You can't use [thing policy variables](https://docs.aws.amazon.com/iot/latest/developerguide/thing-policy-variables.html) (`iot:Connection.Thing.{{*}}`) in the `Resource` section for this permission. For more information, see [Discovery authentication and authorization](greengrass-discover-api.md#greengrass-discover-auth).

#### awsiot.greengrass\_discovery.DiscoveryException: ('Error during discover call: response\_code=404', 404)
<a name="greengrass-discovery-python-issue-not-found"></a>

<a name="troubleshooting-greengrass-discovery-not-found-issue"></a>You might see this error in the following cases:<a name="troubleshooting-greengrass-discovery-not-found-issue-list"></a>
+ The client device isn't associated to any Greengrass core devices or AWS IoT Greengrass V1 groups.
+ None of the client device's associated Greengrass core devices or AWS IoT Greengrass V1 groups have an MQTT broker endpoint.
+ None of the client device's associated Greengrass core devices run the [client device auth component](client-device-auth-component.md).

<a name="troubleshooting-greengrass-discovery-not-found-solution"></a>Check that the client device is associated to the core device to which you want it to connect. Then, check that the core device runs the [client device auth component](client-device-auth-component.md) and has at least one MQTT broker endpoint. For more information, see the following:<a name="troubleshooting-greengrass-discovery-not-found-solution-links"></a>
+ [Associate client devices](associate-client-devices.md)
+ [Manage core device endpoints](manage-core-device-endpoints.md)
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)

### Greengrass discovery issues (AWS IoT Device SDK v2 for C\+\+)
<a name="greengrass-discovery-cpp-issues"></a>

Use the following information to troubleshoot issues with Greengrass discovery in the [AWS IoT Device SDK v2 for C\+\+](https://github.com/aws/aws-iot-device-sdk-cpp-v2).

**Topics**
+ [aws-c-http: AWS\_ERROR\_HTTP\_CONNECTION\_CLOSED, The connection has closed or is closing.](#greengrass-discovery-cpp-issue-no-response)
+ [aws-c-common: AWS\_ERROR\_UNKNOWN, Unknown error. (HTTP 403)](#greengrass-discovery-cpp-issue-forbidden)
+ [aws-c-common: AWS\_ERROR\_UNKNOWN, Unknown error. (HTTP 404)](#greengrass-discovery-cpp-issue-not-found)

#### aws-c-http: AWS\_ERROR\_HTTP\_CONNECTION\_CLOSED, The connection has closed or is closing.
<a name="greengrass-discovery-cpp-issue-no-response"></a>

<a name="troubleshooting-greengrass-discovery-no-response-issue"></a>You might see this error if you specify an inactive AWS IoT certificate in the request.

<a name="troubleshooting-greengrass-discovery-no-response-solution"></a>Check that the client device has an attached certificate, and that the certificate is active. For more information, see [Attach a thing or policy to a client certificate](https://docs.aws.amazon.com/iot/latest/developerguide/attach-to-cert.html) and [Activate or deactivate a client certificate](https://docs.aws.amazon.com/iot/latest/developerguide/activate-or-deactivate-device-cert.html) in the *AWS IoT Core Developer Guide*.

#### aws-c-common: AWS\_ERROR\_UNKNOWN, Unknown error. (HTTP 403)
<a name="greengrass-discovery-cpp-issue-forbidden"></a>

<a name="troubleshooting-greengrass-discovery-forbidden-issue"></a>You might see this error if the client device doesn't have permission to call `greengrass:Discover` for itself.

<a name="troubleshooting-greengrass-discovery-forbidden-solution"></a>Check that the client device's certificate has a policy that allows `greengrass:Discover`. You can't use [thing policy variables](https://docs.aws.amazon.com/iot/latest/developerguide/thing-policy-variables.html) (`iot:Connection.Thing.{{*}}`) in the `Resource` section for this permission. For more information, see [Discovery authentication and authorization](greengrass-discover-api.md#greengrass-discover-auth).

#### aws-c-common: AWS\_ERROR\_UNKNOWN, Unknown error. (HTTP 404)
<a name="greengrass-discovery-cpp-issue-not-found"></a>

<a name="troubleshooting-greengrass-discovery-not-found-issue"></a>You might see this error in the following cases:<a name="troubleshooting-greengrass-discovery-not-found-issue-list"></a>
+ The client device isn't associated to any Greengrass core devices or AWS IoT Greengrass V1 groups.
+ None of the client device's associated Greengrass core devices or AWS IoT Greengrass V1 groups have an MQTT broker endpoint.
+ None of the client device's associated Greengrass core devices run the [client device auth component](client-device-auth-component.md).

<a name="troubleshooting-greengrass-discovery-not-found-solution"></a>Check that the client device is associated to the core device to which you want it to connect. Then, check that the core device runs the [client device auth component](client-device-auth-component.md) and has at least one MQTT broker endpoint. For more information, see the following:<a name="troubleshooting-greengrass-discovery-not-found-solution-links"></a>
+ [Associate client devices](associate-client-devices.md)
+ [Manage core device endpoints](manage-core-device-endpoints.md)
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)

### Greengrass discovery issues (AWS IoT Device SDK v2 for JavaScript)
<a name="greengrass-discovery-javascript-issues"></a>

Use the following information to troubleshoot issues with Greengrass discovery in the [AWS IoT Device SDK v2 for JavaScript](https://github.com/aws/aws-iot-device-sdk-js-v2).

**Topics**
+ [Error: aws-c-http: AWS\_ERROR\_HTTP\_CONNECTION\_CLOSED, The connection has closed or is closing.](#greengrass-discovery-javascript-issue-no-response)
+ [Error: Discovery failed (headers: [object Object]) { response\_code: 403 }](#greengrass-discovery-javascript-issue-forbidden)
+ [Error: Discovery failed (headers: [object Object]) { response\_code: 404 }](#greengrass-discovery-javascript-issue-not-found)
+ [Error: Discovery failed (headers: [object Object])](#greengrass-discovery-javascript-issue-forbidden-not-found)

#### Error: aws-c-http: AWS\_ERROR\_HTTP\_CONNECTION\_CLOSED, The connection has closed or is closing.
<a name="greengrass-discovery-javascript-issue-no-response"></a>

<a name="troubleshooting-greengrass-discovery-no-response-issue"></a>You might see this error if you specify an inactive AWS IoT certificate in the request.

<a name="troubleshooting-greengrass-discovery-no-response-solution"></a>Check that the client device has an attached certificate, and that the certificate is active. For more information, see [Attach a thing or policy to a client certificate](https://docs.aws.amazon.com/iot/latest/developerguide/attach-to-cert.html) and [Activate or deactivate a client certificate](https://docs.aws.amazon.com/iot/latest/developerguide/activate-or-deactivate-device-cert.html) in the *AWS IoT Core Developer Guide*.

#### Error: Discovery failed (headers: [object Object]) { response\_code: 403 }
<a name="greengrass-discovery-javascript-issue-forbidden"></a>

<a name="troubleshooting-greengrass-discovery-forbidden-issue"></a>You might see this error if the client device doesn't have permission to call `greengrass:Discover` for itself.

<a name="troubleshooting-greengrass-discovery-forbidden-solution"></a>Check that the client device's certificate has a policy that allows `greengrass:Discover`. You can't use [thing policy variables](https://docs.aws.amazon.com/iot/latest/developerguide/thing-policy-variables.html) (`iot:Connection.Thing.{{*}}`) in the `Resource` section for this permission. For more information, see [Discovery authentication and authorization](greengrass-discover-api.md#greengrass-discover-auth).

#### Error: Discovery failed (headers: [object Object]) { response\_code: 404 }
<a name="greengrass-discovery-javascript-issue-not-found"></a>

<a name="troubleshooting-greengrass-discovery-not-found-issue"></a>You might see this error in the following cases:<a name="troubleshooting-greengrass-discovery-not-found-issue-list"></a>
+ The client device isn't associated to any Greengrass core devices or AWS IoT Greengrass V1 groups.
+ None of the client device's associated Greengrass core devices or AWS IoT Greengrass V1 groups have an MQTT broker endpoint.
+ None of the client device's associated Greengrass core devices run the [client device auth component](client-device-auth-component.md).

<a name="troubleshooting-greengrass-discovery-not-found-solution"></a>Check that the client device is associated to the core device to which you want it to connect. Then, check that the core device runs the [client device auth component](client-device-auth-component.md) and has at least one MQTT broker endpoint. For more information, see the following:<a name="troubleshooting-greengrass-discovery-not-found-solution-links"></a>
+ [Associate client devices](associate-client-devices.md)
+ [Manage core device endpoints](manage-core-device-endpoints.md)
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)

#### Error: Discovery failed (headers: [object Object])
<a name="greengrass-discovery-javascript-issue-forbidden-not-found"></a>

You might see this error (without an HTTP response code) when you run the Greengrass discovery sample. This error can occur for multiple reasons.
+ <a name="troubleshooting-greengrass-discovery-forbidden-issue"></a>You might see this error if the client device doesn't have permission to call `greengrass:Discover` for itself.

  <a name="troubleshooting-greengrass-discovery-forbidden-solution"></a>Check that the client device's certificate has a policy that allows `greengrass:Discover`. You can't use [thing policy variables](https://docs.aws.amazon.com/iot/latest/developerguide/thing-policy-variables.html) (`iot:Connection.Thing.{{*}}`) in the `Resource` section for this permission. For more information, see [Discovery authentication and authorization](greengrass-discover-api.md#greengrass-discover-auth).
+ <a name="troubleshooting-greengrass-discovery-not-found-issue"></a>You might see this error in the following cases:<a name="troubleshooting-greengrass-discovery-not-found-issue-list"></a>
  + The client device isn't associated to any Greengrass core devices or AWS IoT Greengrass V1 groups.
  + None of the client device's associated Greengrass core devices or AWS IoT Greengrass V1 groups have an MQTT broker endpoint.
  + None of the client device's associated Greengrass core devices run the [client device auth component](client-device-auth-component.md).

  <a name="troubleshooting-greengrass-discovery-not-found-solution"></a>Check that the client device is associated to the core device to which you want it to connect. Then, check that the core device runs the [client device auth component](client-device-auth-component.md) and has at least one MQTT broker endpoint. For more information, see the following:<a name="troubleshooting-greengrass-discovery-not-found-solution-links"></a>
  + [Associate client devices](associate-client-devices.md)
  + [Manage core device endpoints](manage-core-device-endpoints.md)
  + [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)

### Greengrass discovery issues (AWS IoT Device SDK v2 for Java)
<a name="greengrass-discovery-java-issues"></a>

Use the following information to troubleshoot issues with Greengrass discovery in the [AWS IoT Device SDK v2 for Java](https://github.com/aws/aws-iot-device-sdk-java-v2).

**Topics**
+ [software.amazon.awssdk.crt.CrtRuntimeException: Error Getting Response Status Code from HttpStream. (aws\_last\_error: AWS\_ERROR\_HTTP\_DATA\_NOT\_AVAILABLE(2062), This data is not yet available.)](#greengrass-discovery-java-issue-no-response)
+ [java.lang.RuntimeException: Error x-amzn-ErrorType(403)](#greengrass-discovery-java-issue-forbidden)
+ [java.lang.RuntimeException: Error x-amzn-ErrorType(404)](#greengrass-discovery-java-issue-not-found)

#### software.amazon.awssdk.crt.CrtRuntimeException: Error Getting Response Status Code from HttpStream. (aws\_last\_error: AWS\_ERROR\_HTTP\_DATA\_NOT\_AVAILABLE(2062), This data is not yet available.)
<a name="greengrass-discovery-java-issue-no-response"></a>

<a name="troubleshooting-greengrass-discovery-no-response-issue"></a>You might see this error if you specify an inactive AWS IoT certificate in the request.

<a name="troubleshooting-greengrass-discovery-no-response-solution"></a>Check that the client device has an attached certificate, and that the certificate is active. For more information, see [Attach a thing or policy to a client certificate](https://docs.aws.amazon.com/iot/latest/developerguide/attach-to-cert.html) and [Activate or deactivate a client certificate](https://docs.aws.amazon.com/iot/latest/developerguide/activate-or-deactivate-device-cert.html) in the *AWS IoT Core Developer Guide*.

#### java.lang.RuntimeException: Error x-amzn-ErrorType(403)
<a name="greengrass-discovery-java-issue-forbidden"></a>

<a name="troubleshooting-greengrass-discovery-forbidden-issue"></a>You might see this error if the client device doesn't have permission to call `greengrass:Discover` for itself.

<a name="troubleshooting-greengrass-discovery-forbidden-solution"></a>Check that the client device's certificate has a policy that allows `greengrass:Discover`. You can't use [thing policy variables](https://docs.aws.amazon.com/iot/latest/developerguide/thing-policy-variables.html) (`iot:Connection.Thing.{{*}}`) in the `Resource` section for this permission. For more information, see [Discovery authentication and authorization](greengrass-discover-api.md#greengrass-discover-auth).

#### java.lang.RuntimeException: Error x-amzn-ErrorType(404)
<a name="greengrass-discovery-java-issue-not-found"></a>

<a name="troubleshooting-greengrass-discovery-not-found-issue"></a>You might see this error in the following cases:<a name="troubleshooting-greengrass-discovery-not-found-issue-list"></a>
+ The client device isn't associated to any Greengrass core devices or AWS IoT Greengrass V1 groups.
+ None of the client device's associated Greengrass core devices or AWS IoT Greengrass V1 groups have an MQTT broker endpoint.
+ None of the client device's associated Greengrass core devices run the [client device auth component](client-device-auth-component.md).

<a name="troubleshooting-greengrass-discovery-not-found-solution"></a>Check that the client device is associated to the core device to which you want it to connect. Then, check that the core device runs the [client device auth component](client-device-auth-component.md) and has at least one MQTT broker endpoint. For more information, see the following:<a name="troubleshooting-greengrass-discovery-not-found-solution-links"></a>
+ [Associate client devices](associate-client-devices.md)
+ [Manage core device endpoints](manage-core-device-endpoints.md)
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)

## MQTT connection issues
<a name="mqtt-connection-issues"></a>

Use the following information to troubleshoot issues with client device MQTT connections. These issues can occur when client devices try to connect to a core device over MQTT.

**Topics**
+ [io.moquette.broker.Authorizator: Client does not have read permissions on the topic](#client-missing-subscribe-permission)
+ [MQTT connection issues (Python)](#mqtt-connection-python-issues)
+ [MQTT connection issues (C\+\+)](#mqtt-connection-cpp-issues)
+ [MQTT connection issues (Java)](#mqtt-connection-java-issues)
+ [MQTT connection issues (JavaScript)](#mqtt-connection-javascript-issues)

### io.moquette.broker.Authorizator: Client does not have read permissions on the topic
<a name="client-missing-subscribe-permission"></a>

You might see this error in the Greengrass logs when a client device tries to subscribe to an MQTT topic where it doesn't have permission. The error message includes the topic.

Check that the [client device auth component'](client-device-auth-component.md) configuration includes the following:
+ A device group that matches the client device.
+ A client device authorization policy for that device group that grants the `mqtt:subscribe` permission for the topic.

<a name="troubleshooting-mqtt-connection-protocol-error-info-links-intro"></a>For more information about how to deploy and configure the client device auth component, see the following:<a name="troubleshooting-mqtt-connection-protocol-error-info-links"></a>
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)
+ [Client device auth](client-device-auth-component.md)
+ [Create deployments](create-deployments.md)

### MQTT connection issues (Python)
<a name="mqtt-connection-python-issues"></a>

Use the following information to troubleshoot issues with client device MQTT connections when you use the [AWS IoT Device SDK v2 for Python](https://github.com/aws/aws-iot-device-sdk-python-v2).

**Topics**
+ [AWS\_ERROR\_MQTT\_PROTOCOL\_ERROR: Protocol error occurred](#mqtt-connection-python-issue-protocol-error)
+ [AWS\_ERROR\_MQTT\_UNEXPECTED\_HANGUP: Unexpected hangup occurred](#mqtt-connection-python-issue-unexpected-hangup)

#### AWS\_ERROR\_MQTT\_PROTOCOL\_ERROR: Protocol error occurred
<a name="mqtt-connection-python-issue-protocol-error"></a>

<a name="troubleshooting-mqtt-connection-protocol-error-issue"></a>You might see this error if the [client device auth component](client-device-auth-component.md) doesn't define a client device authorization policy that grants the client device permission to connect.

<a name="troubleshooting-mqtt-connection-protocol-error-check-cda-configuration"></a>Check that the client device auth component's configuration includes the following:<a name="troubleshooting-mqtt-connection-protocol-error-cda-configuration-checks"></a>
+ A device group that matches the client device.
+ A client device authorization policy for that device group that grants the `mqtt:connect` permission for the client device.

<a name="troubleshooting-mqtt-connection-protocol-error-info-links-intro"></a>For more information about how to deploy and configure the client device auth component, see the following:<a name="troubleshooting-mqtt-connection-protocol-error-info-links"></a>
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)
+ [Client device auth](client-device-auth-component.md)
+ [Create deployments](create-deployments.md)

#### AWS\_ERROR\_MQTT\_UNEXPECTED\_HANGUP: Unexpected hangup occurred
<a name="mqtt-connection-python-issue-unexpected-hangup"></a>

<a name="troubleshooting-mqtt-connection-protocol-error-issue"></a>You might see this error if the [client device auth component](client-device-auth-component.md) doesn't define a client device authorization policy that grants the client device permission to connect.

<a name="troubleshooting-mqtt-connection-protocol-error-check-cda-configuration"></a>Check that the client device auth component's configuration includes the following:<a name="troubleshooting-mqtt-connection-protocol-error-cda-configuration-checks"></a>
+ A device group that matches the client device.
+ A client device authorization policy for that device group that grants the `mqtt:connect` permission for the client device.

<a name="troubleshooting-mqtt-connection-protocol-error-info-links-intro"></a>For more information about how to deploy and configure the client device auth component, see the following:<a name="troubleshooting-mqtt-connection-protocol-error-info-links"></a>
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)
+ [Client device auth](client-device-auth-component.md)
+ [Create deployments](create-deployments.md)

### MQTT connection issues (C\+\+)
<a name="mqtt-connection-cpp-issues"></a>

Use the following information to troubleshoot issues with client device MQTT connections when you use the [AWS IoT Device SDK v2 for C\+\+](https://github.com/aws/aws-iot-device-sdk-cpp-v2).

**Topics**
+ [AWS\_ERROR\_MQTT\_PROTOCOL\_ERROR: Protocol error occurred](#mqtt-connection-cpp-issue-protocol-error)
+ [AWS\_ERROR\_MQTT\_UNEXPECTED\_HANGUP: Unexpected hangup occurred](#mqtt-connection-cpp-issue-unexpected-hangup)

#### AWS\_ERROR\_MQTT\_PROTOCOL\_ERROR: Protocol error occurred
<a name="mqtt-connection-cpp-issue-protocol-error"></a>

<a name="troubleshooting-mqtt-connection-protocol-error-issue"></a>You might see this error if the [client device auth component](client-device-auth-component.md) doesn't define a client device authorization policy that grants the client device permission to connect.

<a name="troubleshooting-mqtt-connection-protocol-error-check-cda-configuration"></a>Check that the client device auth component's configuration includes the following:<a name="troubleshooting-mqtt-connection-protocol-error-cda-configuration-checks"></a>
+ A device group that matches the client device.
+ A client device authorization policy for that device group that grants the `mqtt:connect` permission for the client device.

<a name="troubleshooting-mqtt-connection-protocol-error-info-links-intro"></a>For more information about how to deploy and configure the client device auth component, see the following:<a name="troubleshooting-mqtt-connection-protocol-error-info-links"></a>
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)
+ [Client device auth](client-device-auth-component.md)
+ [Create deployments](create-deployments.md)

#### AWS\_ERROR\_MQTT\_UNEXPECTED\_HANGUP: Unexpected hangup occurred
<a name="mqtt-connection-cpp-issue-unexpected-hangup"></a>

<a name="troubleshooting-mqtt-connection-protocol-error-issue"></a>You might see this error if the [client device auth component](client-device-auth-component.md) doesn't define a client device authorization policy that grants the client device permission to connect.

<a name="troubleshooting-mqtt-connection-protocol-error-check-cda-configuration"></a>Check that the client device auth component's configuration includes the following:<a name="troubleshooting-mqtt-connection-protocol-error-cda-configuration-checks"></a>
+ A device group that matches the client device.
+ A client device authorization policy for that device group that grants the `mqtt:connect` permission for the client device.

<a name="troubleshooting-mqtt-connection-protocol-error-info-links-intro"></a>For more information about how to deploy and configure the client device auth component, see the following:<a name="troubleshooting-mqtt-connection-protocol-error-info-links"></a>
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)
+ [Client device auth](client-device-auth-component.md)
+ [Create deployments](create-deployments.md)

### MQTT connection issues (Java)
<a name="mqtt-connection-java-issues"></a>

Use the following information to troubleshoot issues with client device MQTT connections when you use the [AWS IoT Device SDK v2 for Java](https://github.com/aws/aws-iot-device-sdk-java-v2).

**Topics**
+ [software.amazon.awssdk.crt.mqtt.MqttException: Protocol error occurred](#mqtt-connection-java-issue-protocol-error)
+ [AWS\_ERROR\_MQTT\_UNEXPECTED\_HANGUP: Unexpected hangup occurred](#mqtt-connection-java-issue-unexpected-hangup)

#### software.amazon.awssdk.crt.mqtt.MqttException: Protocol error occurred
<a name="mqtt-connection-java-issue-protocol-error"></a>

<a name="troubleshooting-mqtt-connection-protocol-error-issue"></a>You might see this error if the [client device auth component](client-device-auth-component.md) doesn't define a client device authorization policy that grants the client device permission to connect.

<a name="troubleshooting-mqtt-connection-protocol-error-check-cda-configuration"></a>Check that the client device auth component's configuration includes the following:<a name="troubleshooting-mqtt-connection-protocol-error-cda-configuration-checks"></a>
+ A device group that matches the client device.
+ A client device authorization policy for that device group that grants the `mqtt:connect` permission for the client device.

<a name="troubleshooting-mqtt-connection-protocol-error-info-links-intro"></a>For more information about how to deploy and configure the client device auth component, see the following:<a name="troubleshooting-mqtt-connection-protocol-error-info-links"></a>
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)
+ [Client device auth](client-device-auth-component.md)
+ [Create deployments](create-deployments.md)

#### AWS\_ERROR\_MQTT\_UNEXPECTED\_HANGUP: Unexpected hangup occurred
<a name="mqtt-connection-java-issue-unexpected-hangup"></a>

<a name="troubleshooting-mqtt-connection-protocol-error-issue"></a>You might see this error if the [client device auth component](client-device-auth-component.md) doesn't define a client device authorization policy that grants the client device permission to connect.

<a name="troubleshooting-mqtt-connection-protocol-error-check-cda-configuration"></a>Check that the client device auth component's configuration includes the following:<a name="troubleshooting-mqtt-connection-protocol-error-cda-configuration-checks"></a>
+ A device group that matches the client device.
+ A client device authorization policy for that device group that grants the `mqtt:connect` permission for the client device.

<a name="troubleshooting-mqtt-connection-protocol-error-info-links-intro"></a>For more information about how to deploy and configure the client device auth component, see the following:<a name="troubleshooting-mqtt-connection-protocol-error-info-links"></a>
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)
+ [Client device auth](client-device-auth-component.md)
+ [Create deployments](create-deployments.md)

### MQTT connection issues (JavaScript)
<a name="mqtt-connection-javascript-issues"></a>

Use the following information to troubleshoot issues with client device MQTT connections when you use the [AWS IoT Device SDK v2 for JavaScript](https://github.com/aws/aws-iot-device-sdk-js-v2).

**Topics**
+ [AWS\_ERROR\_MQTT\_PROTOCOL\_ERROR: Protocol error occurred](#mqtt-connection-javascript-issue-protocol-error)
+ [AWS\_ERROR\_MQTT\_UNEXPECTED\_HANGUP: Unexpected hangup occurred](#mqtt-connection-javascript-issue-unexpected-hangup)

#### AWS\_ERROR\_MQTT\_PROTOCOL\_ERROR: Protocol error occurred
<a name="mqtt-connection-javascript-issue-protocol-error"></a>

<a name="troubleshooting-mqtt-connection-protocol-error-issue"></a>You might see this error if the [client device auth component](client-device-auth-component.md) doesn't define a client device authorization policy that grants the client device permission to connect.

<a name="troubleshooting-mqtt-connection-protocol-error-check-cda-configuration"></a>Check that the client device auth component's configuration includes the following:<a name="troubleshooting-mqtt-connection-protocol-error-cda-configuration-checks"></a>
+ A device group that matches the client device.
+ A client device authorization policy for that device group that grants the `mqtt:connect` permission for the client device.

<a name="troubleshooting-mqtt-connection-protocol-error-info-links-intro"></a>For more information about how to deploy and configure the client device auth component, see the following:<a name="troubleshooting-mqtt-connection-protocol-error-info-links"></a>
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)
+ [Client device auth](client-device-auth-component.md)
+ [Create deployments](create-deployments.md)

#### AWS\_ERROR\_MQTT\_UNEXPECTED\_HANGUP: Unexpected hangup occurred
<a name="mqtt-connection-javascript-issue-unexpected-hangup"></a>

<a name="troubleshooting-mqtt-connection-protocol-error-issue"></a>You might see this error if the [client device auth component](client-device-auth-component.md) doesn't define a client device authorization policy that grants the client device permission to connect.

<a name="troubleshooting-mqtt-connection-protocol-error-check-cda-configuration"></a>Check that the client device auth component's configuration includes the following:<a name="troubleshooting-mqtt-connection-protocol-error-cda-configuration-checks"></a>
+ A device group that matches the client device.
+ A client device authorization policy for that device group that grants the `mqtt:connect` permission for the client device.

<a name="troubleshooting-mqtt-connection-protocol-error-info-links-intro"></a>For more information about how to deploy and configure the client device auth component, see the following:<a name="troubleshooting-mqtt-connection-protocol-error-info-links"></a>
+ [Configure cloud discovery (console)](connect-client-devices.md#configure-cloud-discovery-console)
+ [Client device auth](client-device-auth-component.md)
+ [Create deployments](create-deployments.md)