Help with Uber App

This will be are first time using Uber. I have a code to save a few dollars, but could not find a place to enter it. Do I need to wait until I’m ready to schedule a ride to enter it. Also I was expecting to put a credit card# in somewhere,so it would be on file.

Apple or Android?

For the iPhone:

At the top left corner, there should be a series of three parallel lines. Click on them. Assuming you're signed in, you should see your name and a menu with Commute, Payment, etc. Click on Payment. There's an option to add a credit card, or link to your Apple pay account. At the bottom, there's a section labelled Promotions, with an option to Add Promo/Gift Code.

Don't have an Android so can't help with that.