Sorry, but our system has no way of handling recurring payments such as a periodic subscription or installment plan. You may want to look into using PayPal's own Recurring Payments solution, either as-is or combined with a purpose-built membership management system such as FrontDeskApp, CheddarGetter, etc. You can use PayPal Recurring Payments at the same time as using E-junkie with PayPal, and they won't interfere with each other at all.