Good day @ThomasDK, thank you for your suggestions! In deed, I have googled a lot to make my team provisioning flow working. In the end it turned out I had a typo on the first page of the custom connector configuration. I think after two days of debugging, I finally noticed this in Graph explorer. Power Automate never gave useful error messages regarding this stupid configuration error... But now everything works fine, I use a combination of MS Graph Batch custom connector and regular Graph API HTTP calls to accomplish the tasks, but I guess it would work with one of both alone, too - I just couldn't figure out how.