Just writing to see if anyone else has attempted to use the SharePoint Online WriteBack connector and run into the same problem below - we've currently seen the same issue in 2 separate Domo/SharePoint instances.
After following the steps in the documentation (plus a few extra steps as the documentation is a little thin at the moment) to configure the credentials and progressing to the next step, the connector fails to retrieve (what I'm guessing to be) a list of Site and Group IDs.

No matter the API permissions we grant in the Azure App Registration module we get a "403 forbidden" error. Looking into the response you can see the error message below

Cheers
Eric