Google declined my card

[BigCake]

I tried registering dev account with my mastercard. They declined the card and I can not make in app purchases as well. Card does works, for test purpose I added 5$ to my steam account. What do I do?

[TetraSky]

Call the number behind your card and ask them if they are the ones who declined the transaction.
It's rarely a case of Google/Steam/Amazon or whoever else refusing the card and more your credit union thinking it might be fraud and thus prevented the transaction.