What to do when camera shows Offline?
1. Reset camera
download the tool from this link and reset the cameras, download IPCamSuite for wifi camera
Then power on all the cameras and connect them to router by network cables. Run the tool and then click on refresh to search all the ipc.
When they appear, choose them and then click on reset camera.
2. Match code, refer to How to add a new camera to NVR By matching code?