Error while calling samples.

Tried to call API though samples (C#) but it always through error "object reference error"
Not sure what I am doing wrong.

Below is the stack trace, it failed in CallAuthenticationHeaders

Able to generate by own secratekey and able to download report and access others APIs using same credentials over here: https://developer.cybersource.com/api/reference/api-reference.html

at CyberSource.Client.ApiClient.CallAuthenticationHeaders(String requestType, String requestTarget, String requestJsonData)
at CyberSource.Client.ApiClient.PrepareRequest(String path, Method method, Dictionary2 queryParams, Object postBody, Dictionary2 headerParams, Dictionary2 formParams, Dictionary2 fileParams, Dictionary2 pathParams, String contentType) at CyberSource.Client.ApiClient.CallApi(String path, Method method, Dictionary2 queryParams, Object postBody, Dictionary2 headerParams, Dictionary2 formParams, Dictionary2 fileParams, Dictionary2 pathParams, String contentType)
at CyberSource.Api.ReportDownloadsApi.DownloadReportWithHttpInfo(Nullable`1 reportDate, String reportName, String organizationId)
at Cybersource_rest_samples_dotnet.Samples.Reporting.CoreServices.DownloadReport.Run() in C:\Users\agarwaly\Desktop\CyberSource Reports\cybersource-rest-samples-csharp-master (2)\cybersource-rest-samples-csharp-master\src\Samples\Reporting\CoreServices\DownloadReport.cs:line 35

Start at src/Samples/Reporting/CoreServices/DownloadReport.cs line 35 and follow the stack trace into ApiClient.CallAuthenticationHeaders and PrepareRequest. Reproduce the DownloadReport sample with the stated credentials and compare its request inputs with the other working API calls. Done means the sample identifies the cause and downloads the report without the object reference error.