I was facing a ‘Not found’ using alias/mod_alias.

Not Found
The requested URL /home/ftp (…..) /index.php was not found on this server.

Alias "/ps/" "/home/ftpuser/ps/"
<Directory "/home/ftpuser/ps/">
    Options Indexes FollowSymLinks
    AllowOverride All
    Require all granted
</Directory>

Apache was searching the file in /var/www/html/home/ftp

File does not exist: /var/www/html/home/ftpuser/ (...) /index.php

To solve it I had to tweak .htaccess and set RewriteBase.

RewriteBase /ps/admin/