Port forwarding on Xfinity with Extender

[LucidLiam]

I'm trying to port forward a server, and when I do, it says "Failure, Check your inputs." I am using a range extender that is connected to the router and my computer is plugged into Ethernet on the range extender, and the network name is the one of the router, not the extender which would have EXT at the end. So my computer thinks I am plugged into Ethernet on the router, but not the extender. Please help, I want to portforward as soon as possible.

 

[LucidLiam]

MERGED QUESTION
Question from LucidLiam : "Xfinity router Extender Portforwarding failure"

When I try to portforward, my router says "Failure, Check your inputs" I am using a extender that my computer is plugged into with Ethernet. My computer thinks its plugged into the router, because of the network name not having a EXT at the end. My computer also has two ipv4 and ipv6 addresses, one ipv4 for the router wifi and another for the router Ethernet. Same with ipv6. Please help, I need to portforward soon.