Hey there! That’s one frustrating situation. Let me try and help:

Have you made sure that you have the nessecary credentials in order to actually create the audience in Meta?

If you are able to create the audience, but you aren’t able to actually advertise/use the audience, it could be because of the size of the audience as Meta requires a certain amount of emailadresses before an audience is actionable.

I, however, believe that your issue may be arising from my initial part of this answer.

I hope you fix it!

/Casper