If your cctv system is showing offline try the following steps.
1.
ensure cable from router to recorder is plugged in correctly
2.
if you have tplink adaptors give them both a reboot by turning them off and back on
3.
reboot your cctv recorder (see video below)
4.
reboot your router (unplug power out then in)
5.
reboot mobile phone and then try accessing from Hik connect app