Setup a template licence read from a file hosted in another server

Imagine the following, i have a full website template that i´m about to sell to a person, but i want to make sure that template will not be used anywhere else. I have imagined something like this: -Let' s call the website i´m selling "Website 1", and the website where the licence is(my website) let´s call it "Website 2" -Website 1 needs a little piece of code in order to work, that code is in a file on website 2(wich i control), and it´s fetched via javascript i guess -Website 2 file that has the code cannot be accessed directly via url in browser, i don´t want ir to be possible to see the source code of the file on website 2. I´m sure this is really easy for people with the right knowledge, so bid accordingly please.