sachithmuhandiram When I look at the logs on the MS side, it shows that it's doing what it's supposed to, but I am not sure.
I went through the directions again, made a new application, gave it the permissions, tried logging in with my admin user (for Office365) and my standard user that I use for incoming/outgoing tickets (not a shared mailbox, we pay for a full user account) and got the same error as the old application.
I have 40+ user accounts on our 365 account so I tried adding other email accounts and received the same error. Also tried opening up every permission possible on the new application. It's 2AM EDT and tickets are piling up...and I don't have an answer for my staff or customers for tomorrow except "don't use it".