Cannot figure out how to set the parent project through the rest api

Hello,

I'm using as a reference the 9.x api documentation at (https://confluence.jetbrains.com/display/TCD9/REST+API).

In there, I can find the right rest command to modify an existing project's parent project:

     Project's parent project: GET/PUT XML

http://teamcity:8111/httpAuth/app/rest/projects/<projectLocator>/parentProject

But!, according to what I can understand, it requires an xml payload and that payload is not documented (or I cannot find it :)).

Can someone help me out?

Thanks
Jose