Teams error 500 ServiceError: 500 - internal server error at the Connector

Something failed inside Microsoft's service while processing your request. The status table lists 500 as code ServiceError with various messages and - unusually - documents no retry: the guidance is to report persistent cases through the developer community channels, in contrast to 502, 503, and 504, which are explicitly retryable with backoff.

Two hygiene points keep a 500 investigation short. First, capture the X-Correlating-OperationId response header the Connector attaches to every response - Microsoft's API reference asks you to include it when reporting, since it indexes their internal log entry. Second, be sure whose 500 you are looking at: your own endpoint returning 500 to inbound activities is a different failure (your bug, debugged with Application Insights per Microsoft's troubleshoot-500 guide) than the Connector returning 500 to your outbound send. The direction of the call tells you which side owns the fix.

HTTP/1.1 500 Internal Server Error
X-Correlating-OperationId: 5f1b3c...

{
  "error": {
    "code": "ServiceError",
    "message": "..."
  }
}

You cannot prevent Microsoft's 500s, but you can be diagnosable: persist operation IDs with every failed send, alert on 500-rate rather than individual events, and keep your own endpoint's 500s separately dashboarded (Application Insights exception queries, as the Azure troubleshooting guide walks through) so the two never blur in an incident.