Your question is Brex-Style Balance Check and Fraud. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Implement a simple version of Brex’s backend (check if card has enough remaining balance to accept incoming transaction) using database. After that, think about fraud detection, if all you have is the information about the transaction.