In the web application development, you may have to integrate PayPal payment API because PayPal is one of the most popular payment method in modern ecommerce online merchants.
In Node.js based applications, there is a simple SDK
https://www.npmjs.com/package/paypal-rest-sdk
$ npm i -s paypal-rest-sdk
Next, you need to create sandbox account on PayPal developer account dashboard https://developer.paypal.com/developer/applications
Obtain client_id and client_secret from the sandbox account and set them in the paypal-rest-sdk configuration.
Details are in the SDK readme or documentation.
Now you can utilize the PayPal RESTful API.
That’s all folks!