Http Flow

I am trying to make Http Post Endpoint With Body That i can reuse in my custom activity , there are no documentation about this type of flows ,
is this applicable ?
and if it is
what is the wrong about this

even when i try the designer part

(I Add Input Variable from Input/Output Screen with the type (primitives->object) *wish could put custom type*
and after i put it in parsed content so i can use it later as i tried in my code version ,
then as soon as i add the next activity everything disconnects and shows multiple errors

Start with the issue's screenshots and the described custom activity flow: an HTTP POST endpoint with a body, an Input/Output object variable, and parsed content. Reproduce the designer behavior by adding the next activity and record the resulting errors and disconnected nodes. Done means the flow remains connected and the request body can be reused, or the missing documentation and unsupported custom-type behavior are clearly identified.

Written by the indexing model from the issue text.