Getting Exception while invoking GetFormXML method in Sample app : Sharepoint 2010

We have installed Nintex form On-premise machine which has SharePoint 2010. Now, we want to get the form on the base of listID and content type id. So, We are using GetFromXML method https://help.nintex.com/en-us/sdks/sdk2013/FormSDK/Topics/SDK_NF_API_REF_GetFormXml.htm


I have integrated Form SDK from the below source code. For authentication purposes, I am using the FormDigest2010 method(https://help.nintex.com/en-us/sdks/sdk2013/FormSDK/Topics/SDK_NF_API_OPS_2010_WWSvcOps.htm).


Get .net source code zip from the below link.
https://help.nintex.com/en-us/sdks/sdk2013/FormSDK/Topics/SDK_NF_API_OPS_NintexFormsPublishExample.htm#Building_and_running_the_sample

I am using this method to get XML form. But when I invoke this WCF API then I got protocol Error. The details, I have attached with this mail.
 // Retrieve the form definition XML from the source environment and then save
            GetFormFromSourceAndSaveToFile();

So, Could you please check the above GetFormXML method for SP 2010. 

Thanks.
Regards,
Swapnil Javal