Here’s a nice little Nuget Package that was created by Sean Cullinan from SKC Technologies!
This library makes it easy to process PayPal IPN data in your WebAPI projects. Simply add the custom InputFormatter to your Startup.cs file when configuring services, setup your controller to accept an object of our PayPalIPNRequest type and invoke the process method. At that point you will have a verified IPN object that you can easily work with as needed to integrate PayPal IPN messages into your application and workflows!