Simple PHP API gives error 500 in Cpanel - php

Question

I followed this tutorial to make a simple API with PHP. It works perfect on my computer. I added some other php files to the source folder and I added a composer package (Firebase/JWT) to the project, so a vendor folder and a couple composer files were created. Now the project folder looks like this:
/
- /plublic
-- .htaccess
-- index.php // requires src/functions.php
- /src
-- connection.php
-- functions.php // requires other src/.php files and JWT from composer
-- panel.php
-- responses.php
- /vendor
-- /composer // and files
-- /firebase // and files
-- autoload.php
.htaccess
composer.json
composer.lock
I uploaded this to my cpanel hosting (at api/) using a subdomain (api.mydomain.com). I made the subdomain with cpanel and first set the root folder to api/public but it didn't work (500 error). Then I tried pointing the subdomain to api/ but that didn't work either. What can I do? I think the problem is in the .htaccess files.
#root .htaccess
RewriteEngine on
RewriteRule ^$ public/ [L]
RewriteRule (.*) public/$1 [L]
#/public .htaccess
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ index.php [QSA,L]
I don't know much about .htaccess or composer, so I didn't move anything of that. Thanks.

Answer 1

It's pretty obvious why it does not work. Look at your rules:
#root .htaccess
RewriteRule ^$ public/ [L]
RewriteRule (.*) public/$1 [L]
The first Rule in your .htaccess file rewrites any request of the root, e.g. www.example.com or api.example.com/ to a subfolder /public.
The second Rule complements this and rewrites any other request to the subdirectory /public, e.g. api.example.com/test to api.example.com/public/test
So, effectively, one of these two rules will always fire.
Since you have set the root of api.example.com already to /public it cannot find a /public/public subfolder; thus, you get an error 500.
To resolve this, you could try to remove both rules in the root .htaccess or you can set the root of /api not to the subfolder.
The public/.htaccess file has a typical single entry point configuration and should be fine.
Always use a fresh browser in incognito mode to test the changes.