How to implement paid functionality in software without hardwiring it into code?

Question

PHP

An opensource web project (for example, a client's office) with installation on a server, there is a standard (free) and advanced functionality (paid):
- When you purchase a license for an extended version of the software, an api key is issued with binding to the API on which the software is installed.
- The key allows you to use the extended version for a limited amount of time (eg 3 months).
- Standard functionality is hardwired into the software code
- Extended functionality is not hardwired into the software code, it works for the user only when the key is activated
Question: how to implement the extended functionality in the software with the condition - not to hardwire it into the code to which the user always has access? Has anyone done this before or knows a way? Thanks to

Answer 1

If you are online, then you are lucky, make the work of paid functionality dependent on your server (for example, perform some tasks there), so that nothing would work without a server. Ideally, obfuscate the interaction (make the code work sequentially on the client, then on the server, then again on the client within the same task, just make sure not to sacrifice speed), so that it would be more difficult to reverse the server than to write your paid functionality again.
In the simplest case, you can implement ALL paid functionality on the server, and only the interface on the client (return to the days of the http rest architecture, well, with an eye to efficiency and responsiveness).

Answer 2

"Sidor Solomonovich, you either take off your cross or put on your panties."
Open source projects do not work on the racket model. Money in open source projects is made on the service.
If you can provide an extended service, sign the client up for it.
If you can't, then don't try to trade open source, provide a SaaS service