I know that the recommended practice to use the custom variable of Paypal buttons is to pass an identifier which is a reference to some data in a database and then when Paypal returns a response, verified that id with its corresponding reference in the database in order to do extra processing,
But my question is, if I save data in the database when the user clicks on the Paypal button, the user gets redirect to the Paypal, how will I know that the transaction was never completed if the user clicks on the back button on his browser? Because if the user does that, I will get no response from Paypal (Completed or not). If I don't have any response from Paypal, then I just saved some data in my database for no reason.
How should I solve this issue?
I have a big form with a lot of fields, so I cannot send all that data in the custom variable since there is a limit.
Please help!