Authentication Failures (401 / Invalid Credentials / Missing OAuth Token) via MID ServerIssue Integrations routed through a MID Server start failing with authentication errors (401, "Invalid username/password combination," "Access token was not provided") even though credentials are valid and the MID Server shows "Validated". Symptoms Users report this as an authentication problem: a flow, Integration Hub action, or REST/SOAP/spoke step that fails with one of: 401 Unauthorized / "Invalid username/password combination""Access token was not provided" (OAuth Bearer token never attached despite a valid, unexpired client_credentials token)"Unable to load connection with alias ID: ..." Troubleshooting the credential itself finds nothing wrong: The same credential/token works independently in Postman or an Outbound REST Message.Connection, Connection Alias, OAuth Provider/Entity Profile/Credential records are all verified correct, no duplicates.The MID Server record shows Status: Up and appears Validated.Typically, the cloned-to instance is affected (e.g., fails in DEV post-clone, still works fine in PROD/UAT). Release All Cause MID agent log shows on every credentials_reload: StandardCredentialsProvider / EncryptedPayloadDecrypter:"Unable to retrieve data from instance. This MID may not be validated."at MIDServerInfoRemote.decrypt(...)Caused by: AutomationIOException The MID Server's local keypair and the keypair the instance expects are out of sync. MID validation only breaks when these two get out of sync. Resolution From the Related Links, click Invalidate on the MID Server record (not Rekey - Invalidate alone clears memory, restarts the MID, and auto-generates a fresh keypair on restart).Wait for Status: Up; re-approve in the MID Server list if prompted.Confirm "Validated At" refreshes to a current timestamp.Recheck the agent log on the next credentials_reload - error should be gone.Retest the original integration - authentication should now succeed. Related Links Validate the MID ServerKB0786475 - MID Servers and ClonesKB3140571 - Midserver is unable to fetch credentials post upgrade to ZP11/AP4