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BugZero found this defect 900 days ago.
When attempting to login to the Veeam Backup for Microsoft 365 Restore Portal, the following error occurs:
At this time, there are two known scenarios that may cause this issue:
Scenario 1: Certificate not added to the Trusted Root Certification Authorities Make sure that the certificate is added to the Trusted Root Certification Authorities. Reference: Authentication Settings
If this issue persists, please create a Veeam Support Case.