Unable to validate SharePoint site URL , getting 401 error in dynamic 365

Hello folks !!

We have dynamic 365 online integrated with SharePoint server2016 on premises from year 2018.

Suddenly in Dec-2021 , after 3 years, we are getting error "You don't have permissions to view files in this location. Contact your Microsoft Teams owner or SharePoint administrator for access." in dynamic 365 , further while debugging found that Dynamic 365 is trying to validate SharePoint site but unable to validate.

 while validating site , getting 401 -unauthorized error.

Below information for reference :

• User has Admin role in dynamic 365 and SharePoint.
• same user has Global admin role in Office 365
• SharePoint site (On -Prem) able to access from browser
• Raised ticket on Microsoft - verified that dynamic 365 online  does not have any issue

Pl. help to solve an issue.

Thanks in advance

Regards,

Dhara Patel