So I tried and the /ombi exists but the webapp isn't loading. I've gone through the documentation and it gives an example:

  <Location /ombi>
 Allow from 0.0.0.0 
 ProxyPass "http://127.0.0.1:5000/ombi" connectiontimeout=5 
 timeout=30 keepalive=on 
 ProxyPassReverse "http://127.0.0.1:5000/ombi" 
 </Location>
 RewriteEngine on 
 RewriteRule ^/ombi$ http://mywebsite.com/ombi/ [R=301,L] 
 RewriteCond %{HTTP_REFERER} 
 "http://mywebsite.com/ombi/" 
 RewriteCond %{REQUEST_URI} !^/ombi 
 RewriteRule ^(.*)$ /ombi$1 [R=301,L]

But this gives an error when embedding in the 000-default.conf on line 31, which is the ProxyPass line. I pasted the code (with own url ofc) in between the <VirtualHost> and </VirtualHost>.