Install the Signplus C# SDK package 
dotnet add package Alohi.Signplus
Call your first SDK method 
using Signplus;
using Signplus.Config;
using Environment = Signplus.Http.Environment;

var config = new SignplusConfig
{
    Environment = Environment.Default,
    AccessToken = "YOUR_ACCESS_TOKEN"
};

var client = new SignplusClient(config);

var response = await client.Signplus.GetEnvelopeAsync("envelope_id");

Console.WriteLine(response);