Why I cannot get the response of insertRecords api method?

Why I cannot get the response of insertRecords api method?

Hi,

I'm using "https://crm.zoho.com/crm/private/xml/Leads/insertRecords?authtoken=MyAuthToken&scope=crmapi&xmlData=Postdata" api to insert record into the ZohoCrm but when i try to make post request I get the responses as " Unable to process your request. Please verify if the name and value is appropriate for the "xmlData" parameter error" and sometimes I get response content type as: text/html instead of text/xml but when I use Postman to post the same url, it works without any problem.  I almost tried all of the paths to post data properly but I faced with these issues as I mentioned above. I'm using ASP .NET so if you share a sample working code with me I would be so glad.  
Please Help me ASAP,
Thanks.