Example: PayPal payment details
When I have one turned on, it changes "for one month" to "for every month" in the form of an extract, so why do I need two of them?
I searched for variables here and cannot find it. https://developer.paypal.com/webapps/developer/docs/classic/ipn/integration-guide/IPNandPDTVariables/#id091EB0901HT
You can view descriptions of these (and any other available options) in the PayPal Standard Variables Documentation .