My Mastercard not connecting with Apple Account on Apple Card?

Sorry, but your question is not clear. Mastercard is not an issuer or bank, they are a payment network processor. Banks issue credit cards, debit cards and prepaid debit cards, and they can be on several payment networks including Mastercard, Visa, American Express, Discover and others if you’re not in the US.

Several years ago Apple did away with the term Apple ID and uses the term Apple Account. Your Apple Account is what is used to pay for goods and services such as subscriptions, videos, apps etc.

So, what exactly are you trying to do and if you’re receiving an error message what exactly does it say?