SharePoint guests can't login even with correct permissions

Hi IBN22​,

Please follow the troubleshooting steps outlined in the article below:

https://learn.microsoft.com/en-us/archive/technet-wiki/52429.sharepoint-online-troubleshooting-we-re-sorry-sign-in-isn-t-working-right-now-but-we-re-on-it-please-try-again-later

If the issue persists after following these steps, you’ll need to raise a support ticket with Microsoft for further assistance.

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If this reply helps you, please consider marking it as the accepted answer.

I’ve had this happen a few times with external users and it’s usually not the permissions in SharePoint itself, it’s the guest account in Entra/AD causing the trouble. Even if they show up with the right permissions, SharePoint might still be pointing at an “old” identity or the invite didn’t get redeemed correctly.

What’s worked for me is:

• Remove the guest everywhere (site permissions, M365 admin, and from Entra including the recycle bin).
• Re-invite them fresh, and tell them to open the invite in a private/incognito window so it doesn’t grab cached credentials.
• Double-check that they’re signing in with the same email you invited.

If you’ve got conditional access policies running, that can also trip them up, so worth checking those too.

Not the most fun fix, but usually after a clean re-invite things start working again.