1. It seems like you cannot forward a different port than the one setup on your server. For instance, your firmware doesn't allow forwarding port 26600 of your WAN IP to port 80 of your local machine. You might want to change the port on which Apache serves its HTTP service before enabling the port forwarding.
To forward ports on the ZyXEL EX3301-T0 router, access its web interface and navigate to the port forwarding or virtual server configuration section. Enter the necessary details such as the port number to forward, the IP address of the device you want to forward the port to, and the protocol (e.g., TCP or UDP). Setup a static IP address on either your computer or device that you want to forward a port to. Login to your ZyXEL Prestige 2602H 61C router. Navigate to the port forwarding section. Click the NAT link. Click Edit Details. Create a port forward entry.