Recently I have been unable to invite guests to my Azure AD. This had been working great for over a year but now I get the error "Generic authorization exception" when trying from Powershell or the Azure Portal. Inviting still works with both methods for those already in the Azure AD (well, the invitee gets the invitation email but not much use since they are already in the Azure AD).
What you suggested worked so thanks. All I can figure is that Azure must have made a recent change in user invitation authorization because this was working for over a year as it was until maybe last week (i.e., the global administrator didn't need this authorization); I may have missed an Azure change notice or perhaps I mistakenly flipped this switch off somehow.