A possible problem would be that your bank does not deal directly with MasterCard, but goes through another company such as CIS. They do the actual dirty work. They can really screw the works up, both in getting your bank on line, and when you actually use Apple Pay. My Bank issues MasterCard debit Cards, handled by CIS, and Visa credit cards, handled by another company. My Visa card was on Apple Pay within a month or two of roll out of the program, but the MasterCard took almost 6 months before the bank was even able to begin testing, and almost another month before I could get my MasterCard into my wallet.
Lately my MasterCard has begun to be declined at merchants that I have used for a long time. My Visa, that I use as a backup has always worked. After very long hours on the phone with Apple and my bank it looked like CIS fixed their problem. Then my MasterCard was declined again last night.
The most frustrating thing is CIS is one of those hidden companies that you can't reach out and wrap your hands around their throat in order to encourage them to do good and proper work.