make sure the deck is on the same subnet as the steam link

from a pc on the same network make sure you can ping the link and deck lan ip
all should be 192.168.same.different

if using wifi, check the router settings and disabled wifi isolation for the ssid you use
also disable any vpn
and on link/deck streaming advanced, make sure allow direct connection is enabled

if those fail, try adding new host on the link, and pairing again with the deck