From Dahua Wiki
DDNS registration failed or can not access the device domain name.
DDNS (Dynamic DNS/DynDNS) is a method of automatically updating a name server in the Domain Name System (DNS), often in Not Real Time, with the active DDNS configuration of its configured hostnames, addresses or other information.
If DDNS is not working properly please try to:
1. Check the device to see if it is connected to the network:
2. Verify that the device has acquired and IP address via DHCP or that a static IP has been assigned.
3. Ensure that you can connect to the system on via the local network:
4. Try to access the system from another device on the network e.g. Try to open the web interface of the device from a web browser on your local network.
5. Check the corresponding protocol of the DDNS is enabled:
6. Log into the DVR/NVR/CVR and navigate to the "Network" menu then look for the DDNS option and check the box to enable the service. After the service is enabled you will need to fill in the required informwation i.e. DDNS Type, Host IP Port (1~65535) Domain Mode Domain Name and Email Address if applicable
7. Check the DDNS credentials at the DDNS site and menu of the system:
8. Please confirm that log in information matches on the Dynamic DNS platform that you are using and also in the DDNS section of the recorder.
9. Default Google DNS server is 18.104.22.168, 22.214.171.124.
10. Use different DNS provided by your ISP.