DIAGNOSIS The robot has trouble with certain modern router settings, specifically 5GHz bands or combined SSIDs (where 2.4GHz and 5GHz share one network name).
FIX Go into your router's settings and temporarily disable the 5GHz band, or create a separate, dedicated 2.4GHz network with a different name. Connect the robot and your phone to that 2.4GHz network during setup. You can re-enable 5GHz afterward.
IF THAT DIDN'T WORK Your phone's connection might be the issue. Forget the WiFi network on your phone, restart your phone, then reconnect to the 2.4GHz network before trying setup again.
HEADS UP The j7+ does not support WPA3 enterprise or certain VPNs. If your network uses these, you'll need a guest network without them for the robot.