Double payment charged to Customer: Once to Paypal and Another via Shopify simultaneously

[CleisDesign]

Hello: 

We have just experienced double payment charges to 2 individual customer orders via paypal and then again via Shopify credit card charge.
Can it be that the customers did this on accident as a user error? Or is there a preventative payment condition I need to set up when using both PayPal express and Shopify/payment cc options? Thanks in advance.  

[Trevor]

Hey, @CleisDesign. 

Great question! The double charge would have been a user error as a double charge would not occur based on the payment methods you have enabled. Paypal requires the user to be redirected to their platform to complete the purchase; whereas Shopify Payments allows them to manually enter in their payment information within the checkout. The user would have needed to both manually enter their credit card information, and log in to Paypal. Though, this should have created two separate orders, and not have been processed on one. 

If you haven't already, I would reach out to the customer to see if this was done in error, or if they intended to make two separate purchases before choosing to cancel and refund one of them. 

Let me know if you have any questions.