Problem description
OSS sent a callback request to the client's callback server, but the server rejected the request.
Causes
The callback server returned a rejection response to OSS's request. This can happen for any of the following reasons:
Network or firewall restrictions: The callback server is not reachable from OSS — for example, the server is behind a firewall or IP allowlist that blocks OSS.
Examples
The following figure shows OSS receiving a rejection from the callback server.
Solutions
Step 1: Check for network or access restrictions.
Confirm the callback server is publicly accessible or that OSS IP addresses are included in any IP allowlist.
Check the callback server logs to identify the exact reason the request was rejected.
Step 2: Verify the callback server implementation.
Make sure the callback server is strictly built according to the example of the official documentation. For the complete server-side implementation specification, see Callback.