Problem with wired connection

I FINALLY got an LAN adapter and Ethernet splitter (since my router only has one Ethernet port) set up so I could play SSBU with a wired connection, but of course things can never be that simple. As I go to connect via wired connection I get an error saying ‘unable to obtain IP address’. So I instead switch to manual connection and input my IP address and DNS settings and try again. This time around I get an error saying ‘could not perform DNS name resolution’. WTAF! Anyone know what could be the problem I’m encountering? Both the LAN adapter and Ethernet splitter are compatible with a switch so I know it’s not that…and yes I connected the adapter in the back of the dock instead of the side