@mohank Have you set static wireless channel on the main router, when setting up the WDS ? If wireless channel is set to Auto, when the main router changes the channel (due to interference, reboot,...

@Martyn7 Use this guide for configuring C7 in AP mode. If you are receive=ing an error message in the Tether app then use a browser.

@Toople Most probably, your DVR needs that port. Here - https://www.cctvcameraworld.com/port-forwarding-for-dvr-and-nvr/ you can read what could it be or better check your DVR manual or manufacturer...

@sanikbug2k18 Here's the procedure in such cases. If after that procedure you still can't access the device then contact your local support and explain these details to be advised.

@sanikbug2k18 What is your device exactly, give here the model and the HW version ? On the bottom of the device there's a sticker with these details.

@sanikbug2k18 If the device is under warranty you can contact the retailer for a replacement. If he can't help, then you should contact your local support to be advised further.