I am using ManageEngine Support center plus API to manage requests through a C# project. 

I am trying to assign and reassign requests, so basically changing supportReps within the same group and sometimes from one group to another.   To do this I am using the "updateRequest" API operation., 

So here's an example of what I want to do:

I have a request R. It is currently assigned to group G1 and supportRep S1. 

I want to assign it to a group G2 and leave supportRep empty. 

For this reasons, I tried setting the supportRep parameter to Null, "None", "Not Assigned", "Unassigned". The result is always the same,  the following error message : "Specified request URI incorrect. Parameters missing" Status code: 4003.

So my question is: Is it even possible to change back a request's group or a request's supportRep to its state of unassigned through the API (because I know it's possible through the web portal)? If the answer is yes, please let me know how to do that.

Many thanks!