Error: Request Security Violation at /

Hi Support,

I do have some quieres which I need help from you.

I am trying to implement Above Acrobat Sign Api for which I am following link https://secure.na1.adobesign.com/public/static/oauthDoc.jsp.

I have successfully able to generate "Code" for Authorize request. After that trying to get Access Token with Access Token Request, as I make post request it return 
"Error: Request Security Violation at /" 

Also, I have tried "https://helpx.adobe.com/sign/kb/how-to-create-access-token-using-postman-adobe-sign.html"

and follow every single steup and end up with 

Please let me know if I am missing something.

After all 
Thanks in Advance.