Error: AADSTS700082 – The refresh token has expired due to inactivity
This typically occurs when the customer tenant has an MFA setting that allows "remember MFA for X days", which breaks token refresh after extended inactivity.
Cause: The “remember MFA” setting bypasses full reauthentication for a time, but Microsoft disables the refresh token after 90 days of inactivity — causing Sync 365 access to fail.
Disable the “remember MFA for X days” setting in the customer tenant:
Wait ~30 minutes after disabling the option and the error should clear automatically.