Registration key in PHP script/website?

Question

PHP

How to make a hidden script in a script that is located in a completely different place that is hard to reach for a regular user? And where is such a place to be found?
I will consider everything using the example of the great VK_API.
For example, there is a script with 3 files:
"index.php" - markup and form for entering account data,
"status.php" - a function for changing the status in a group and in an account,
"sms.php" - Sending a message to the user's LAN.
Actually, my task is to make sure that I can sell this script without fear of a drain.
I imagine it like this: I register/buy 2 hosting/websites. scripts.ru and key.ru
on scripts.ru I upload the script itself (3 files "index.php", "status.php", "sms.php"), on key.ru I create the file "check_key.php" and check the key that should receive into the form key.
Now I am creating a "script.php" file, which will actually be sold. In it I am making the function of sending a request to key.ru with two parameters, the key that the buyer will enter in the input field and the full URL of the site from which this request comes. After that, it works "check_key.php" and it checks the URL and the key in the database, and if the key and the URL are in the database, then it connects scripts.ru...
It seems that this is how I imagine it .... I wrote this scheme to make it clearer what exactly I want. If it's not difficult, please tell me how it's actually easier to implement,

Answer 1

Store the scripts on your server and make an access API based on them, that's all