If there is an interface via OWS, they can do whatever they want on their website to accomplish this. OWS has the ability to return deposit requirements as configured in
OPERA both an availability request as well as on the create booking message. Customer can use that info to tell how much they need to collect and then redirect
their guest, either prior of after confirming the booking to PayPal, Amazon, or any provider they chose.
Once they get the payment confirmation from the vendor, they can insert the actual payment in the OPERA reservation via the MakePayment message.