How to set additional parameters in http service


I am trying to make a call to rest API url.

I am using the http service to pass the url and string data.

The url format is like this:<payload_string>

This works in the IE browser but when I put this in http url. It says illegal character. Do I need to pass the additional parameters like the Action and MessageBody seperately. If yes, How do I do it?

I used args document but was not successful.

Please help!
Thanks again.