@BenediktPM 

Hi, thanks for posting question here.

If you have enabled remote management for TP-Link 4G LTE Router but are still unable to access its web interface remotely, please follow the troubleshooting steps below:

    1. Verify if Internet IPv4 Address is a public IP address or not. (Check it on Advanced -> Status -> Internet part)

       If not, it means you are behind CGNAT, please contact your ISP to see if they could assign you a public IP address.

    2. Make sure you've configured remote management settings correctly. You may refer to the configuration guide.

    3. Make sure you've entered correct address when trying to access it remotely.Correct address should be http://Internet IPv4 addess:port number or "https://InternetIPv4 address:port number".

    4. Configure DDNS if the Internet IPv4 address is not static IP.

For more details about the troubleshooting, please refer to this FAQ.