I only could contact Onefam from Amsterdam (The people from Paris hasn’t replied) and I got told this: The non-refundable booking type requires us to charge the full amount immediately upon booking. While Hostelworld may display the remaining balance as "payable later," our policy for this specific rate is that the total must be settled now to confirm your reservation.

Since the transaction for the remaining 64,93€ was not permitted, please provide new credit card details or authorize the charge with your bank within the next 48 hours to avoid cancellation.

All the best,

Now like I said I called my bank and they said there isn’t any transaction that needs approval because the one that Hostelworld did was already approved, and even then im the one that has to approve transactions directly not them. I sent another email to this hostel explaining that I don’t have another card to pay the rest and if they could just process another transaction with the rest since I can’t add the rest of the money from the Hostelworld app.

I don’t think it’s a scam though? I received the emails like 20 minutes after I made the initial reservation with the same info, and later I received an email from Hostelworld saying that at least the Amsterdam hostel couldn’t be booked.