RestSharp is a powerful library to automate REST API using C#. Here you can find important part of RestSharp and how to automate your REST API tests. I have used NewtonSoft Json.NET to serialize and deserialize JSON.
Project has two helper classes to manage your framework in better way
API Helper - Helper Class to manage RestSharp
Reporter - Reporter Class to manage reporting using Extent Report
You can go through videos here if you like https://www.youtube.com/watch?v=Y2L6rOJGu6w&list=PL_GzuQ9GmG0EYtFSyODKjFG0Ldvl178-u
I have course on Udemy which covers in depth. Here is course link https://www.udemy.com/course/rest-api-testing-using-csharp-restsharp-and-specflow/?referralCode=813AC01FB87297C87E5C