If a payment doesn't show up in your transaction history, it depends on what the merchant told you:
If the merchant confirmed the payment went through
Wait a little while, it can sometimes take a few minutes to appear. If it still hasn't shown up after 30 minutes, contact support in the app and we'll look into it.
If the merchant said the payment didn't go through
The transaction likely didn't reach us. Check with the merchant to confirm, and if needed, try paying again or use a different payment method.