Teams error 405 Method Not Allowed: 405 - operation not supported by the channel

The Connector API reference documents 405 as "The channel doesn't support the requested operation." The Connector is a multiplexer over many chat platforms, and not every operation in the REST surface is implemented by every channel; when a bot calls one Teams (or another connected channel) does not support, the answer is 405 rather than a silent no-op.

A second, humbler source produces the same status: pointing the wrong HTTP verb at your own or Microsoft's endpoints - for example a health check that GETs /api/messages (which only accepts POST) will see your own framework's 405, and a reverse proxy that rewrites POST to GET manufactures the inbound version. Distinguish by whose error body accompanies the status: a Connector ErrorResponse means the platform refused the operation; an HTML or framework-flavored body means the request never reached the Bot Framework at all.

Retrying a 405 is pointless in both variants - the method or capability will be just as unsupported on the next attempt - so the correct handling is to remove the call or gate it behind the channel check described below.

HTTP/1.1 405 Method Not Allowed

{
  "error": {
    "code": "MethodNotAllowed",
    "message": "The channel doesn't support the requested operation."
  }
}

Gate channel-specific features on the channel ID of the incoming activity instead of assuming the full Connector surface everywhere. Keep an integration test that exercises each operation your bot uses against Teams specifically, so an unsupported call fails in CI. The endpoint verb mix-up is covered from the webhook side in webhook debugging.