Weird behavior on reverse proxy by htaccess

I've set up a reverse proxy on my vps by placing the following .htaccess file under /var/www/html/ecommerce/app.

DirectoryIndex disabled

RewriteEngine On 
RewriteRule ^(.*)$ http://127.0.0.1:3000/$1  [P,L] 
RewriteRule ^$ http://127.0.0.1:3000  [P,L]

localhost:3000 is the local node server running on my vps. /var/www/html/ is the document root. So I was expecting, if all goes well, I can load the app via http://my-public-vps-ip/ecommerce/app . But that doesn't work and instead I can load the app via http://my-public-vps-ip:3000 . I don't understand this. Could you help me understand what might be going on?