Are you attempting to implement a REST Service similar to Pega 7.1's Pega API?

See:  https://community.pega.com/sites/default/files/help_v72/procomhelpmain.htm

Also:  In the upper right of the Developer Portal you can click the "Resources" icon to launch the Pega API Landing Page, 

If your REST Service is having trouble receiving a POST, what does the received JSON look like?

Perhaps the format is incorrect.

You can try adding "Param.<PropertyName>" in the "Map To Key" field of the query string in the POST Request form.

Hi pedel,

Even after giving the property reference as Param.Request in map key.The value is disappearing once we save or chin in the rule.

Could you please suggest i am using pega7.1.7 version for service rest Post implementation.