How can I use Postman to replicate SAML post made by Kentor test idP?

Question

I am trying to use Postman to make a SAML 2 Post. This imitates what the post request from http://stubidp.kentor.se/ sends to our Service Provider for SAML authentication. However, the Postman Request always returns an error. Is there any additional requirements in the Post?

Senator