After doing a complete wipe and fresh install of 12.8.5 (w/ hotfix), and after re-authorizing each incoming and outgoing mailbox, I'm still getting occasional access errors. I did find out that: 1, you need to paste in the secret again, and 2, you (apparently) need to auth the outbound first, then the inbound, because if you don't, you'll need to re-auth inbound after you do outbound. So after doing that, I'm still getting errors, but not consistently.
Error processing mailbox messages: OAuth token request failed (statusCode: 401 UNAUTHORIZED): invalid_client [7000215] AADSTS7000215: Invalid client secret provided. Ensure the secret being sent in the request is the client secret value, not the client secret ID, for a secret added to app '0dc7cb84-f640-4ab5-b158-7cf990cd64ae'. Trace ID: 3e69ff4c-e7ef-4e56-9bcb-8c248db40d00 Correlation ID: 97d32e11-554b-4ba6-87a3-5081bb21c763 Timestamp: 2025-03-31 15:28:24Z
Here's a screenshot:
