Can my customers pay part of the cost now and the rest later on my white label travel portal?

Yes, a white label travel portal can be set up to take a part payment now and collect the balance later, but whether you can offer it on a particular booking depends on the supplier behind that booking rather than on the portal.

The way it normally works is that the portal takes an agreed share of the total at the time of booking, records the booking as part paid, and stores the balance with a due date. Your customer gets a confirmation that shows what has been paid and what is still owing. When the balance falls due you can send them a payment link, or your staff can take the money in the office and mark it received, and the booking then shows as fully paid in your reports. This suits holiday packages, tours and hotel stays that you are holding on your own terms, because you control when the money has to reach the supplier.

Where it becomes harder is with airline tickets and prepaid hotel rates. In most cases the ticket is issued straight away and the airline or the consolidator wants the full fare at that moment, so there is nothing left for you to collect later unless you carry the balance yourself. The same is true of many hotel rates that are charged at the time of booking. Your payment gateway also has to allow a second charge or a follow up link, and on some plans part payment is an option that has to be switched on before it appears at checkout.

Decide which of your products you actually want to sell this way, then check with the supplier for those products and with your payment provider that a later collection is allowed, and make sure your own terms on the portal state clearly when the balance must be paid before travel.