Might be this - https://developer.milestonesys.com/s/article/Creating-a-Configuration-Backup-or-a-Configuration-Report-fails-with-the-error-message-The-SQL-user-does-not-have-the-necessary-permissions-to-access-the-backup-folder
If my guess does not fit please ask the Support Community.
As this is not related to software development with the MIP SDK, which is the focus of this forum, please ask again in the support community, you should get better help from the partners using the support community.
https://force.milestonesys.com/support/MccSupportCommunity