Apple in-app purchase

I made an in-game purchase while my debit card had enough funds but the amount wasn’t charged instantly, then I used my debit card for another purchase and now I don’t have enough for the in-game purchase I already made. What happens if I don’t recharge the card? The state of the purchase in the App Store says pending, I received the in-game currency and used it and my bank wasn’t billed for the purchase.

To note that I eventually did recharge my card but the purchase is still pending and the card was billed for the amount, but my question is what would happen if I hadn’t? And when will the payment be complete?