Hik vision one camera showing offline

Hi all,

I have installed a 3 camera system and can view all 3 cameras from the hard drive and also off the pc through ivms 4200 but when I go on hik connect on my iPhone one camera shows offline. I can go on play back on my phone and you can play back it will just not play a live view and shows off line. Any help would be appreciated.
Thanks in advance
Mike.