Some organisers, depending on the price of their exhibitor packages, may select to offer you a deposit scheme i.e. paying in two installments. They do this on the proviso that come the balance due date you will pay the remainder balance on time. They have suppliers to pay!
Once you have completed your application, click save and you will be taken to Your Order page where the Deposit option will be there for you on the Order area itself. Just select the option you need, then recalculate the order, if your computer/device does not do this automatically. Then click Apply now.