It sounds like you are referring to a PayPal Credit installment plan. It's the merchant who decides to offer instalment plans through their website, and not PayPal. With selected merchants, when you check out with PayPal Credit, we’ll show you a selection of instalment offers, enabling you to spread the cost of your purchase across a number of payments.
Subject to application, merchant and status, these instalment offers allow you to choose a set number of monthly payments of differing amounts and at varying interest rates. If you already have PayPal Credit, you can take advantage of these offers without having to reapply as long as you have enough available credit limit.