Redirect all subdomains to another file - .htaccess

Question

My greetings to all.
I have a problem for which I am looking for a solution.
I have an my-website.com site and every user who registers on my site gets a personal link: USERNAME.my-website.com .
Meanwhile, I had the following rule in my htaccess :
RewriteEngine On
RewriteCond %{HTTP_HOST} ^(.*)\.my-website\.com [NC]
RewriteRule (.*) process.php/$1 [L]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule (.*) index.php/$1 [L]
How to make all sub-domains ( USERNAME.my-website.com ) point to process.php ( process.php/USERNAME ) file and that the others urls like my-website.com/OTHER point to index.php/USERNAME ? ( in case OTHER is not a file or a folder of my site )
Here's what I did, but it doesn't work.

Answer 1

"But it doesn't work" is a bit vague, so all we can do is given some general advice and suggestions...
First you need to make sure that those subdomains are actually served at all by your http server. You did not write anything about that, nor how you host your site at all.
Also you obviously have to take care that distributed configuration files (".htaccess") are considered at all by your http server, also something which is not clear from your question.
Given both of those aspects you will indeed have to concentrate on your rewriting rules. Here is a variant of your own implementation with a few changes:
RewriteEngine On
RewriteCond %{REQUEST_URI} !^/process\.php$
RewriteCond %{HTTP_HOST} ^(.*)\.my-website\.com [NC]
RewriteRule ^ /process.php/%1 [QSA,END]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !^/index\.php/?
RewriteRule ^/?(.*)$ /index.php/$1 [QSA,END]
You probably will have to make some more changes. But based on the vague information you gave it is hard to be more specific.
A good way to start debugging issues with rewriting is to enable rewrite logging inside your http server. That allows to closely monitor what is actually happening inside your rewriting engine. Please consult the documentation about that: https://httpd.apache.org/docs/current/mod/mod_rewrite.html