On your iPad log into your NVR using the IP address
Go to configuration, advanced and set Access Platform Mode at the top to HiLookVision, that should populate the address with something like litedev.eu.hilookview.com then just add an encryption password.
Whilst with your NVR on the first page (system i think) there is a very long serial number, ignore the WCVU at the end and write down the 9 characters before them (my one was AB1234567 type format).
Go to the hikvision app on your phone, add device manually, adding type is Hik-connect domain and enter the serial number you wrote down and it should find your nvr. If it asks for a code type in the password you did earlier.
Once added it should automatically show on the main Page of the hik vision app.
Then test it works by switching off your phone Wi-Fi and use 4G.
hopefully that fixes it?