Summary
A customer's account must have an email address for a Stripe credit card payment to go through. Otherwise, you will get this error message when when trying to charge a customer's card on file:
Stripe charge Cannot proceed payment
Key Points
Enter the customer's email address in the customer's Billing page
If the customer doesn't have an email address, enter yours in the customer account
Enter an email address so Stripe can send the customer a receipt. If your customer doesn't have an email address, enter your own and it will process the card. You can the print the receipt and give it to the customer.
An email address requirement is Stripe's requirement.