iDrive backup for Mac failing
I would keep on the vendor to explain how to debug this sync failure.
If they don’t make you happy, the team that make a ARQ software has a history of resolving issues for their clients (in my circle of Mac admins and consultants).

https://www.arqbackup.com/

If you’re technical and prefer command line, I can’t recommend rsync.net highly enough either. Their price point is attractive as is the detailed logging capabilities for troubleshooting - if you can set it up, you can troubleshoot it easily. Go for arq if ease of setup is your preference.

https://rsync.net/products/attic.html