I have a recurring payment solution set up via PayPal's IPN service, basically the user fills in a form, pays the money and via IPN my system gets a ping to grand the user access to the system.
Everything technically works fine, but occasionally on the last day of a user's cycle they forget that it is a recurring payment and complete the form again. PayPal doesn't seem to mind this and creates a second recurring payment profile.
Currently I go in, refund the money and cancel this new payment profile, but obviously this isn't ideal - is there any way I can configure PayPal to not accept new profiles from people with currently active profiles? Or will I need to catch this at my website's end and do some form of lookup before allowing the payment?
Paypal did not recognize the a transaction is a duplicate one, It tackles the transaction as a new transaction. You will have to tackle it from your system. When implementing payment gateways, It is good approach to save the billing with a status pending or something in your system before sending to payment gateway. Also in the form user is filling you can implement a field to uniquely identify the user like his email address and you can also save the expiry or second recurring date against the user unique field in your system. Now when the user enter the same unique field and want to submit a form again you can validate that the same user is paying again but its expiry of second billing date is not yet reached, so prompt and restrict him for paying again.
Hope it will help you.