Well, I am developing a script which I want to ask when installing a unique ID that without the ID & not work .. something like BB, IP, XenForo, etc.
It is always difficult & how getting and researching that violate the code, but how could I?
So you want them to have to enter a key on install and without it they can't install it?
You would have to have a database on your site that adds keys on purchase and have the install script check the database for the key.
But, I'm not sure if it's really worth the hassle because just like vB or IPB it will end up nulled if people want it.
If the same thing, but reading other comments & as I have given can be encrypted with ZenGuard or something like it.
What of the database I have it covered, but what I do is not checking.