Do my customers have to pay the whole amount at the time of booking, or can I take a deposit and collect the rest later?

Yes, taking a deposit and collecting the balance later is possible, but it is not something you can switch on for every booking, so it is worth understanding where the limit sits. Part payment is under your control only when the money is under your control. For a holiday package you have put together yourself, or a tour you operate, you decide the deposit, the balance and the date it falls due, and your portal can show the traveller what is left to pay.

Where it stops being your decision is anything you are reselling. A flight that has to be ticketed straight away has to be paid for straight away, because the airline takes the full fare from you at the moment the ticket is issued. Hotels are more mixed. Some rates are pay at the property, some are pay now and non refundable, and some allow a hold with payment later. In each of those cases the supplier sets the rule and your portal follows it rather than overriding it.

There is also a cash flow point worth thinking through before you offer deposits widely. If you take a small deposit but the supplier bills you in full at booking, the difference comes out of your own working capital until the customer settles up. Many agencies handle this by offering deposits only on their own packages and on travel that is far enough out.

Go through the products you actually sell most, work out which ones let you defer payment and which do not, and set your deposit rules only on the ones that genuinely allow it.