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A2A Connector 2.0 Troubleshooting

To troubleshoot Anypoint Connector for A2A (A2A Connector), become familiar with the information about performing general troubleshooting, addressing specific common errors, and interpreting commonly thrown exception messages.

Error Unmarshalling String JSON Payload into Type io.a2a.spec.Task. Cause: Argument "content" is Null

Likely cause:

  • The payload maps to a task or message schema that expects a non-null text content field, but received null.

Resolution checklist:

  • Ensure every text part includes a non-empty text value.

  • Avoid sending content: null or equivalent nullable fields in message or task parts.

  • Validate outbound JSON in Studio using connector metadata types before sending.

  • Confirm your DataWeave transformation outputs JSON objects, not quoted JSON strings.

Failed to Establish SSE Connection

Likely causes:

  • Request is sent as a non-streaming SendMessage instead of SendStreamingMessage (JSON-RPC), or to POST /message:send instead of POST /message:stream (HTTP+JSON).

  • The server app doesn’t include an active A2A Server - Task Listener flow.

  • The agent card does not advertise capabilities.streaming: true.

  • Reverse proxy or gateway strips text/event-stream semantics or closes long-lived HTTP connections.

Resolution checklist:

  • Verify the method is SendStreamingMessage (JSON-RPC) or the request targets POST /message:stream (HTTP+JSON).

  • Verify the server flow includes an A2A Server - Task Listener. The unified task listener serves streaming requests. There is no separate A2A Server - On Task Stream Listener in 2.0.

  • Confirm the agent card advertises capabilities.streaming: true.

  • Confirm HTTP 200 response with Content-Type: text/event-stream.

  • Check timeout and keepalive settings in intermediary proxies and load balancers.

A2A Server Config Errors Despite Correct Configuration

Likely causes:

  • Invalid Agent Path to listener route binding.

  • Card file path not found at runtime.

  • Agent card JSON is malformed or missing capability metadata expected by clients.

Resolution checklist:

  • Use ${app.home}/agent-card.json when deploying to CloudHub.

  • Validate card JSON syntax and required top-level fields.

  • Confirm <a2a:connection listenerConfig="…​" agentPath="…​"/> references a valid http:listener-config.

  • Check app startup logs for binding or card parsing errors before runtime requests.

See Also

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