PayPal allows for one IPN URL to be set for a PayPal account.
If someone trying to purchase states they are getting a message from PayPal saying they already have a recurring payment set up, it might be because they have purchased a membership from another site you are using PayPal with.
WishList Member provides on IPN Forwarding option in the PayPal integration. This allows the forwarding of an IPN to multiple URLs.
This means one PayPal account can be used on multiple WishList Member sites.
Please Note: WishList Member needs to have the IPN enabled in PayPal.
The PayPal Checkout integration allows you to enter the URL(s) to forward the IPN to.
An IPN URL can be set by logging into your PayPal account and navigating to the Instant Payment Notification section.
This is found in the My Profile > Selling Tools > Instant Payment Notifications section.
You can ensure IPN is enabled and set your desired IPN URL there.