Paying entry fees and finding your invoice
Your invoices are listed under "My Invoices" on your main menu: one per entry, or combined if the program groups them. Make a payment from "My Payments"; if the program is running a promo code or discount, there's a field to enter it during checkout.
If a discount you expected doesn't apply, double-check it hasn't expired or that your entry actually qualifies (some discounts need a minimum number of entries on the one invoice, or only apply within a date window). If it still looks wrong, contact the program organiser, only they can adjust or apply a discount manually.