POST method gives me 405, but GET won't print results. POST works locally.

Hello everyone, I’m trying to make something small for my personal use. There are tools like this online, but after I’ll be done with it, I want to write an algorithm which will solve everything without all those if inside of process.php.

Anyway, can you look at those two files, they are really short, why can’t GET method print anything?

Project is here:

Live is:

I don’t know a lot about PHP but most of the times when something like this isn’t working for me I use the Network tab in the Chrome DevTools. Did you try that?