DHTMLX Scheduler possibilities

I still try to verify if I can use DHTMLX Scheduler for .Net in a potential project we try to win.

The project have to be usable with all devices (mobile or computer).
So we decide to create a Web Form project with a view dedicated to each device.
We are realizing a Proof Of Concept (POC).

We have to add server-side rules to limit the actions of the users.
For example, a user cannot add an event on the scheduler if another event exists for the same period in a particular state.

How can we develop this kind of rules and call them from the client-side code?

In our POC, we add a button to the lightbox to change some state of the event but we can only call javascript method.

How can we call code-behind method from the javascript method we add for the new button?

From js code, assigned to the button you can trigger any serve side action, by ajax call

function runOnClick(){ dhtmlxAjax.post(model/validate", "value="+scheduler.getEvent(id).property, function(result){ var response = result.xmlDoc.responseText; alert(response); }); );