Hi @Kw23,

According to the translation of Google Translate, I think that your question is DDNS not working normally. If there is any discrepancy, please describe it in English.

May I know if your network topology diagram is as follows:

Cable modem—router )))((( client devices

(Note: — stands for wired connection,)))((( stands for wireless connection )

Firstly, please confirm that you have set DDNS correctly. You may log in to router's web management interface and go to Advanced > Network > Dynamic DNS > Select a DDNS service provider and configure it.
For more configuration details, please refer to: How to set up TP-LINK DDNS on TP-Link Wireless Router (New Logo) 
Additionally, here are some tips for you if you are having trouble accessing the local server remotely via DDNS:
    1) Make sure the Port Forwarding settings are configured properly, make sure you are able to access the local server via the current public IP address of the Router.
    2) Use "nslookup your_ddns_name" or "dig your_ddns_name" on Windows/Mac OS to verify if the DDNS is working properly.
    3) For detailed troubleshooting, please refer to this FAQ: General Troubleshooting For DDNS on a TP-Link Wi-Fi Router 
If the issue persists even when all settings are correct, please contact us with the result of the above troubleshooting steps.