question

Hello!
I have difficulty to start using RingCentral Api.
My application type is "Public" and my Platform Type is "Server/Web".
I am using C# to authorize but I got Bad Request and the following answser:

{
  "error" : "unauthorized_client",
  "error_description" : "Unauthorized for this grant type",
  "errors" : [ {
    "errorCode" : "OAU-251",
    "message" : "Unauthorized for this grant type"
  } ]
}

I saw that it is because my Platform Type (Server/Web) does not support password grant type and I need to use "OAuth 2.0 Code flow". 

I tried to find an example using "OAuth 2.0 Code flow" in C# but did not find anything. Could you please give me an example that works for me?

Thank you very much!