Trouble forwarding port 51820

[meazz1]

I have installed PiVPN and want to setup port forwarding for 51820. I'm having some difficulties. For some reason, I can't access my server from outside. It's timing out.
I know the server behind my router is working because I used to have EdgeRouter X in the past and simple port 80, 443 worked for this setup.

This is my setup now,

192.168.4.0/24
Pi VPN 192.168.4.8
My Nextcloud server is on 192.168.4.3
I have a domain name setup for the Nextcloud server.