The Viva gateway requires an available standard ethernet port on the router. When connecting the gateway, make sure that the port does not serve a special purpose, for instance "Television" or "IP telephony".
The ports needed are 443/TCP outgoing, which is used by SSL/TLS (i.e. internet traffic), as well as 8883 which is registered for MQTT over TLS.
Note: Even though typically these ports are open, Viva has received information some TP-Link routers have 8883 closed.