Have you been able to load the cameras in Hik-Connect before?
What are the model numbers of the cameras and DVR that you're having problems with?
Is the firmware for everything up to date?
Are you using Hik-Connect on Android or iOS? Which version of the app are you running?
Have you added the device to your account through the Hik-Connect web portal, using the method in this guide? - How to use Hik-Connect