So I had an interesting call with a rep today about this benefit. He said, with absolute certainty after being questioned by me numerous times, that you do not have to choose an airline provider. You can simply make your purchases and then call Aspire and they will apply the credit. He even said you could apply credits to many different airlines, not just one chosen one. He said if you do enroll in a single one online then you do not need to call for any credits to this chosen airline, but you still could call if you have charges on other airlines and would receive credits for those. This is the first time I've ever had a card with this particular benefit, so I was surprised to hear it. Is this everyones understanding of the benefit?

Anyway - OP - re the online enrollment for both the Airline Credit and Priority Pass - although the website shows red verbiage saying it is unavailable, simply ignore it and continue on with the enroll button. It will allow us to enroll regardless of said verbiage (which the phone rep confirmed with me while I was speaking with him). He was able to see my online choices in real time.