When I checkout using PayPal express checkout, it returns an error message
PayPal gateway has rejected request. Payment has already been made for this InvoiceID (#10412: Duplicate invoice)
I have tried to reset everything but still get the same error.
How to solve this issue?
Best Answer
It is because the same Invoice ID has been submitted to the same PayPal business account. This always happens on dev server as the Invoice ID always reset due to re-installation.
Workaround - Allow Duplicate Invoice
Profile > Payment Receiving Preferences
Block accidental payments > allow multiple payments per invoice ID