Sending Post-Data to a URL with using the RPCManager and Smartclient (LGPL)

[fes]

I am using Smartclient version 8.1 (LGPL) and I am trying to send some data per POST from a form to a URL via the RPCManager.

var data=form.getValues();
isc.RPCManager.sendRequest({
    data:data,
    httpMethod: "POST",
    useSimpleHttp: true,
    evalResult: true,
    actionURL:' .$ajax_url. ',
    callback:
    function (rpcResponse, data, rpcRequest) {
        alert("response from the server: " + data); 
    }
});

I am using this Code but nothing seems to be sent. I am using Smartclient with Javascript and Json files. Maybe you can help me!
Thank you!

[fes]

Ok, I just tried around a bit and after I gave the data via the "Params" Attribute like this:

 params: data,

it sent the data as GET. Now my only Question is, how I can make the RPCManager to send the params as Postdata. I have httpMethod set to "POST".
Any guess?