When Soapbox processes a transaction with Stripe, no Customer record is created unless that transaction is a recurring donation in the Donations app. All one-time donations, event registrations, and Shop purchases will only create Payment records in Stripe with no Customer record.
If a recurring donation is processed for a new donor, Soapbox will create a Customer, Subscription, and Payment Method record. The credit card used for the recurring donation will be set as the default Payment Method for the Customer as well as the Subscription.
If a recurring donation is processed for a donor whose email address matches that of an existing Customer in Stripe, Soapbox will create a new Subscription and Payment Method record and associate each with that Customer. The credit card used for the recurring donation will be set as the specific Payment Method for the new Subscription and no change will be made to the default payment method for the Customer.