"Customer support" is a joke. Uber Eats is great at sending promotions/discounts to their customers. Redeeming and actually being able to use them are, however, another story. FYI, if your promo/discount auto-applies to your order, should you go back to change or even reconfirm your order, the promo will no longer be added automatically. Same with changing your form of payment; if you change it after accessing checkout but before placing the order, any previously applied discount is gone.