Porting RT::Client::Rest

I’m developing a port of module RT::Client::Rest in C++, and I’m in trouble
with ticket actions (take, steal, untake),
Login, Logout, Get Ticket and Search are ok.
Reading the original code in Perl, I found that in RT::Client::Rest any of
this ticket actions are done by the post
of a multipart/form-data to URL http://rtserver/REST/1.0/ticket/1/take with
one parameter named content and “Action: take” as its value,
but I’m getting this response :
RT/3.4.5 409 Syntax Error

action: Unknown field.

Action: take

What are the correct post parameters to use with RT REST interface?

Thanks in advance.