Problem in connecting to Zephyr Scale to fetch Test Related Data

[gouris]

I have Jira in cloud and extension of Zephyr Scale added to it for Test Related Issues.

I am using ZephyrScale.Rest.Sdk NuGet package Version 1.0.0.6. I am using Visual Studio 2019 C# code. The code is provided in the NuGet package but it gives me internal server error. I have created Zephyr Scale API key as per documentation and using it for connection. The connection is being created using 

var zService = new ZephyrScaleCloudService("app url", "user api token");

the error is "$exception {"Could not communicate with the Zephyr server. Response code: InternalServerError, Response Body: {\"error\": \"No value present\"}"} System.Exception"

I tried using Postman but it also gives same error. "500 Internal Server Error": No value present

Help needed