The DDNS concerns several factors:
1 WAN IP, is it a public IP?
2 Port forwarding on the NAT. Have you set it correctly?
3 port forwarding on the device itself. Can you access the device locally with the port number?

For my understanding, DDNS consider the following:
1.Register an account from No-ip.
2. Make sure modem is working in bridge.
3. Remote management has been enabled on the TP-LINK if you want to DDNS to the router itself. If there is a camera or a server behind the router, you need to open ports for it on the router.
4. After the port forwarding, you need to use the WAN IP of the router +port number to view it.
5. Use DDNS to view.