I've set up a basic promo code for all users to be able to use once. The promo code works fine on a desktop browser. When I try the promo code on a mobile browser, I can't access the 2nd page of my checkout process. After I've entered the promo code and selected continue, the same page reloads. I don't get any errors or anything. If I remove the promo code and select continue, the 2nd page loads fine.
I'm using EE 2.8.1 and Expresso Store 2.5.1