Short article today, so we’ve been dealing with the new OneDrive guest B2B Sync which is a feature currently in preview, we followed all of the initial setup instructions yet it still wouldn’t work.
We would constantly receive “Sorry, OneDrive can’t add your folder right now” when trying to sync a library which the guest user had full access to. After 4 hours on a call with Microsoft support and verifying every setting we could possibly think of I noticed a limitation which we had initially missed.
The reason turned out to be fairly simple and an oversight on our part, but it’s something many of you can easily fall into if you are following the latest Microsoft best security practices.
Multi-Factor Authentication from an external organization is not yet supported. Only guest accounts that don’t require MFA will sync.B2B Sync – OneDrive – https://docs.microsoft.com/en-us/onedrive/b2b-sync
The only solution currently is to disable MFA requirements on guest and external users, assuming you’re enforcing this via Conditional Access policies you can disable this whilst still keeping MFA for your users by modifying the relevant policy, selecting ‘Users and Groups’ and then in the Exclude Tab select “All guest and external users”.
However, this will reduce the security of your tenant so proper thought needs to be put into this decision.