You can add your payment gateways in your "Payments" page.
There are different types of PayPal accounts you can apply for. The supported accounts on plug&paid are Merchant (Premier/Business) and Individual (Student/Personal) accounts. If you have a Merchant account your buyers can benefit from PayPal's Express Checkout* services.
Express Checkout allows merchants and developers to minimize the number of steps customers must complete when they checkout. It is designed for merchants who don't have an Internet Merchant Account for processing credit and debit card payments. Buyers can pay with PayPal or credit and debit cards. Buyers can checkout without leaving the merchant's site via a PayPal window that overlays the merchant's site. The merchant's site remains visible in the background. Additionally, you can use PayPal Checkout with One Touch, which is now automatically included on all eligible transactions.
Choosing the Right Account Type: https://www.paypal.com/us/selfhelp/article/does-paypal-offer-different-types-of-accounts-faq2347
Stripe checkout now supports Bancontact, iDeal, GiroPay, Sofort, P24, Alipay and multiple other payment methods. These payment gateways will automatically be allowed to use in plugnpaid once you attach a Stripe Account. Make sure that the payment method you are planning to use is also activated in your Stripe dashboard.