True, security is important, but it's an example that's meant as a starting point and to give him an idea of how it can be done.

If someone knows the address to the current PHP/TXT examples, they can easily show the coupon codes in the browser. You'll have to work with the security to find a safe method to use it.

Either that, or find another, more secure, method. Working with online files, especially without a secure connection or password protection can be very unsafe.

I would recommend that you just send them a coupon code when they buy your game instead of trying to connect through 3dgs.