Can I give my customers a discount code to use at checkout on my portal?

Yes, in most cases you can create your own discount codes and let customers type them in at checkout, although how much control you get over the rules depends on your plan and on how your portal has been set up.

The usual way it works is that you create a code in your admin area, decide whether it takes off a percentage or a fixed amount, and set a start and end date so it stops working on its own. Many setups also let you limit a code to one type of product, such as hotels only, or stop the same customer using it again and again. If you sell through sub agents, you can normally decide whether the code is for your direct customers only or whether your agents can pass it on too.

The honest limit is that the discount comes out of your own margin, not out of the supplier's rate. Your suppliers send a net rate, you add your markup on top, and a discount code simply reduces what the customer pays at the end. Airlines and hotel suppliers will still invoice you the same amount, so if a code is worth more than the markup you added, you end up selling that booking at a loss. Some fares also have to be shown exactly as the supplier provides them, which is why a code is normally applied to the final total rather than to the fare itself.

Before you promote a code anywhere, check what markup you currently have set, then create one test code, run a test booking and look at what actually lands in the final total and in your reports.