PHP-GPIO VS Whoops

For PHP I'd use https://github.com/ronanguilloux/php-gpio and if you truly want to make it safer on security use a JSON Web Token https://en.wikipedia.org/wiki/JSON_Web_Token but honestly if it's a DIY solution on your LAN, no DMZ, I wouldn't even bother. At least I wouldn't start with that. If it works and you keep it running after weeks then yes, improve it including with security constraints.

To get the full control of the error output (or, rather, of the error message handling) I would suggest to use an exception handling function, set_exception_handler() I've got an example in my article on PHP error reporting. There, instead of just spitting out the raw exception, you can use the Exception class methods to get the relevant parts and either log or echo them out, depends on the server role. Or you can even include a library like Whoops that dramatically improves the output.

Check out spatie/laravel-ignition (if using Laravel) or filp/whoops

I've been using whoops but it's a bit stale (not even 7.x or 8.x native, just compatible with those but still very much 5.x code). Might have to explore ignition.

To give an example of what I am looking for, there is this library for PHPT: http://filp.github.io/whoops/

You're correct about it being a faulty webpage, but that's now what any browsers devtools look like. What you're seeing here is a whoops error page from an older version of Laravel.