Hi @michaelxipderas
The problem you face is the result of an open bug with our Stripe extension, which is scheduled to be fixed with the 4.3.2
release in early February 2020. The problem here is that when a customer makes a purchase in the test mode, and then when the same person tries doing it in the live mode, it shows up the error. You can read more on this issue here: https://github.com/woocommerce/woocommerce-gateway-stripe/issues/1092
A possible solution is to delete the customer from the Stripe customer list in https://dashboard.stripe.com/test/customers
If that doesn’t work, you can try deleting the customer account you used for testing from Users > All Users.
With that said, the error occurs only when you try making a purchase in the live mode using the same user that tried testing in the test mode.
If you want to test purchases, you can use a different email id/user account for purchases. This would help you test live purchases in your site. Additionally your (potential) customers won’t have any troubles making purchases from your site.
In the meantime, let us know if you have questions. We are happy to help!