Can I create a discount code that my customers type in at checkout to get money off their booking?

Yes, promotion codes are a normal part of travel agency software, though exactly what you can set up depends on your plan and on which products you are selling. You create the code yourself in your admin area and decide the rules behind it, such as whether it takes off a fixed amount or a percentage, which products it applies to, the dates it runs between, and how many times it can be used in total or per customer. Your customer then types the code on the payment page and the reduction shows on the total before they pay.

The part worth thinking about carefully is where that discount comes from. The supplier still charges you their full price, so a promotion code is really you giving away part of your own markup. If you set a generous code against a product you are selling on a thin margin, you can end up making nothing or paying out of your own pocket without noticing straight away. Many setups let you protect yourself by applying codes only to selected suppliers or products, or by requiring a minimum booking value before the code works.

There are also limits that come from the supplier rather than from the software. Taxes and supplier fees usually cannot be discounted, and some fares and rates are sold on terms that do not allow you to alter the price your customer sees. Where that applies, the code will simply not take effect on that item.

Before you launch a promotion, check your margin on the products you want to include and set the code to expire on a fixed date so it cannot keep running after your sale ends.