THANK YOU @NigelG! You definitely led me in the direction I desperately needed. Ended up being this that did the trick:
(Changed the scope to:
https://www.googleapis.com/auth/business.manage https://www.googleapis.com/auth/userinfo.profile
And changed the User profile endpoint to:
APIs are definitely tricky but I’d be lying if I said I didn’t do a dance & shout for joy when it finally worked 
Gracias amigo!