If you only have a few products with fixed prices, integrating PayPal is a matter of defining a button for every product in their UI, copy the HTML form that is

If you only have a few products with fixed prices, integrating PayPal is a matter of defining a button for every product in their UI, copy the HTML form that is generated next to the button and then submit a POST request to PayPal to have the user start the PayPal checkout flow. Stripe's new checkout system works similar. You define products in their UI and submit a request with the according SKU. The advantage of PayPal is that it requires zero JavaScript. It's just a POST request. Of course, you need to listen to PayPal's IPNs to process a payment on the server, but this is exactly the same effort as with Stripe.