If you have Uber Cash on your account, it can be applied to trip fares and cancellation fees. You can always see how much Uber Cash you have on your account by selecting "Payment" from your app menu.
If you want to change the payment method to/from Uber Cash:
1) Enter your destination on the home screen
2) Tap on your payment method or Uber Cash below the vehicle selection
3) On the Ride Profiles screen tap 'Change' next to the payment method
4) Select the payment method you wish to use
Please note that once the trip has been requested, you cannot switch the payment method. If you wish to switch your payment method, tap HELP in your app to let us know. We'll be happy to switch it for you.
If you don't have enough Uber Cash to cover your ride, you'll be given the option to buy just enough to cover your ride, or buy a set amount of Uber Cash and receive a discount on the purchase.