If you have recently seen this error while trying to place an order, do not fret ! It is just a weirdo thing caused by PayPal. We don't store credit card info on our servers, it is stored remotely by Paypal (even if you are paying by credit card). They only hold the info for one year before they purge it, so you just need to delete and reenter your card number to fix the error !
PayFlow API call failed
Error Code: 19
Detailed Error Message: Original transaction ID not found