Open the transaction in your activity to see the reason. The most common ones:
Not enough balance. The purchase plus the fee was more than the balance across your accounts. Top up and try again.
Card locked. Unlock your card in the app.
Over a limit. A single purchase can be between $1 and $2,000. Your card also has a spending limit for any rolling 24-hour period. For most cards it's $25,000, and the app shows your own limit.
Negative balance. If a previous payment took your balance below zero, card payments are paused until you top up.
The merchant doesn't accept Visa.
Check your balance and card status in the app, then try again.