Using Shop Reward Discount Codes

Has anyone had problems using the Shop Discount Codes they redeemed from rewards? I try and use them and they say either invalid through the app or on the website it only allows me to apply one code. I can’t find anywhere that you can’t use multiple codes. Thanks for the help guys!

You can’t stack codes, so only one per transaction, and you can’t use on sale items, only full priced items.