You don't say what transfer protocol you are using, I'm assuming HTTP.
HTTP uses TCP/IP, so your device NAT needs to redirect the connection request to your server.
There's others ways, like if you have more than one internet IP address, so the requests could be directed to the server too, but thats more complicated than port forward so I think its not what you have.
So basically you need to configure the port forward. Take it like a PABX, calls from the exterior lines needs to know a ramal to reach a phone, thats a distant mean to think of it.
And as said, the suggestions you said, are not intended for that, is mainly for client connection, what for many NAT is not necessary, as the NAT is prepared for doing that.