A promo code is a kind of coupon that entitles you to additional value/discounts/cash returns. Customers who have a promo code can get discounts by entering the code when purchasing a ticket. TicketGateway provides promotional codes and access code for costumers, which are created by the promoter. If you are a promoter you can create as many promo codes as you want for your event tickets.
Access codes are used to access the hidden tickets from the event. There is no discount for these codes. The codes are created when the organizer wants particular tickets to be available to only people who know that specific access code.