Error: This payment method (affirm) is not activated for the account specified in 'on_behalf_of". You can only create testmode affirm Paymentintents. You can learn more about this here https://support.stripe.com/questions/i-am-having-trouble-activating-a-payment-method

The error was received when the customers attempted to checkout by credit card. The shop does NOT have Affirm as a setup gateway.

Customers were attempting to checkout through the app, and were attempting to use coupon codes.