Thanks for the response Jen, as always! I've seen this post and pretty much everything else you can find on the subject by googling, forums and stackOverflow. I've been trying everything I can think of with no success.
I've tried (and am still trying) to change certs, new certs, new app; trying everything I can think of.
It works perfectly on my own phone, that I've deployed directly from computer. But when I send to apple itunnesConnect, and allow users to install the app using testflight, they don't even get that initial alert saying "...Do you allow this app to send you notifications blah blah blah "
I'm thinking of ways to be able to debug, to see what's going on with the firebase.init, if the callback is being called or not.
Any ideas or suggestions would be appreciated.