It would be helpful if you could create a Stripe model (StripeCustomer for example) with an initializer. Although all of the models right now are structs, one easy way in Xcode to generate initializers is to make them classes temporarily and generate member wise initializer.

<img width="765" alt="Screen Shot 2020-02-13 at 6 59 53 PM" src="https://user-images.githubusercontent.com/12012815/7

Little feedback is given to the user if they do not enter their credit card information correctly. See Stripe's list of credit card numbers that can be used for testing to throw certain errors.