Here are some of the key aspects of port forwarding. As the guide mentions: port forwarding maps an external IP : external port to internal (i.e. OpenSprinkler’s) IP : internal (i.e. OpenSprinkler’s) port.
1. The external port can be almost any number you want to assign (as long as it doesn’t conflict with other ports if you are port forwarding other devices).
2. The internal port must match OpenSprinkler’s port. By default this port is 80, and there is no need to change it actually. The only reason you would want to change it is if your router requires the external port and internal port to be exactly the same, and you don’t want 80 to be the external port. This is unusual as most modern routers allows the external port to be independent of the internal port.
3. Your external IP address has to be a public IP (i.e. reachable over the Internet).
If you still can’t solve the problem, submit a support ticket and we can help you. I’ve called several users and walked them through the setup and they all successfully set up port forwarding in the end.