How to forward router web interface through VPN

Question

I'm accessing a remote Ubuntu Server using SSH over a VPN. Now I would like to configure the remote server.

I tried to forward incoming traffic on port 80 of my tunnel to the router address but it's not working:

sudo iptables -A FORWARD -i tun0 -o enp3s0 -p tcp --syn --dport 80 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -i tun0 -o enp3s0 -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A FORWARD -i enp3s0 -o tun0 -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -P FORWARD DROP

sudo iptables -t nat -A PREROUTING -i tun0 -p tcp --dport 80 -j DNAT --to-destination 192.168.1.1
sudo iptables -t nat -A POSTROUTING -o tun0 -p tcp --dport 80 -d 192.168.1.1 -j SNAT --to-source 172.20.20.11

I also have a web server running on port 8080 so I tested with that address instead and it was working so I don't know why it's not working for the router interface:

sudo iptables -A FORWARD -i tun0 -o enp3s0 -p tcp --syn --dport 80 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -i tun0 -o enp3s0 -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A FORWARD -i enp3s0 -o tun0 -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -P FORWARD DROP

sudo iptables -t nat -A PREROUTING -i tun0 -p tcp --dport 80 -j DNAT --to-destination 192.168.1.197:8080
sudo iptables -t nat -A POSTROUTING -o tun0 -p tcp --dport 80 -d 192.168.1.197 -j SNAT --to-source 172.20.20.11

UFW firewall is inactive

Network Configuration:

adm@server:~$ ifconfig
enp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.197  netmask 255.255.255.0  broadcast 192.168.1.255
        ether f4:4d:30:6b:a2:8c  txqueuelen 1000  (Ethernet)
        RX packets 21987  bytes 22287960 (22.2 MB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 14821  bytes 2654314 (2.6 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

tun0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST>  mtu 1500
        inet 172.20.20.11  netmask 255.255.255.0  destination 172.20.20.11
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 100  (UNSPEC)
        RX packets 2761  bytes 134743 (134.7 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 2523  bytes 936758 (936.7 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0