Uber Eat taking my promo code

I used my FNB promo code on Uber eats, mind you it is my first time using Uber Eats. Then when I had app**** my promotion code it said I used the wrong payment details for the promo, so I changed it to my correct account, but after I changed it my promotion code was not available and I could not enter it again because I had already entered it. What a disappointment for a first time Uber Eats user! It is a complete fail