MainModule and PrivateModule, how to use them?

Hi guys!

So I recently got into this ModuleScript business and I'm quite interested..

Let's say I'm working for this kid who pays me on a monthly basis in return for usage of my scripts, and he ends up not paying me after 3 months. I would be able to completely disable my scripts if I were to link all my scripts to my PrivateModule.

Now my question is; How the hell do I link them?

I've created a simple MainModule script with the following code:

local module = {}

    function module.test()
            print("Working Module!")
    end

return module

This ModuleScript was named "MainModule" and uploaded as a Model to ROBLOX. I copied the ID and pasted the following code into my NORMAL script:

module = require(ID_HERE)
module.test()

I published my game, but whenever I try to test the scripts in studio I get the error "Unable to find module for asset id" in my output, and I see no print from the ModuleScript.

Is there any way for me to fix this issue? I would honestly love to use this type of script, but for some reason I just cannot manage to get it to work..

Another question about these scripts is; How do I make sure only I can access this ModuleScript (Refering to the kid who didn't pay up)? I want to save my MainModule as a ROBLOX Module, be able to update it in my own games, and then have it update on other games where it's linked aswell via the require code.

Thanks!