If a top-up failed, it may show as pending on your main bank’s side for up to 5 business days. We send the reversal to your card issuer instantly, so as soon as their system processes it, your balance should also be updated.
In cases like this, it's always better to confirm your top-ups from recent days: you can count how many times you were charged in your online banking and how many top-ups were successful in Revolut.
Most likely, you won't see a failed top-up in your bank transactions' list at all - most banks do not display such instances. This way, you may not notice that your balance got updated when you received the funds back.
Please keep in mind that most banks process top-ups with delays, so a top-up showing today could, in fact, be the one made 2 days ago.