DDNS on my GL-XE300 doesn't work

Hey,
Ioday I tried to activate DDNS as base of an VPN-Connection. I activated DDNS in Applications and I got a Hostname, but if I click on DDNS Test the result is a message like:
The IP from DDNS domain resolution is not the same as the WAN IPs of the device. You need an Internet Public IP address to use the Dynamic DNS. If this router is behind NAT, you may need to set up port forward in your ISP router. If you have VPN Client enabled, please disabled "Services from GL.iNet Use VPN" in the global options.

Just for Information: I have a public IP address from my mobile provider O2 and my router is not behind any other device.

BR
ETHVH

If you do a test from somewhere else (like nslookup or something similar) does the DDNS domain returns your public IP? How sure are you about the public IP address? It's pretty rare to have one in an mobile contract.

Yes, I made a lookup to my ddns name and I received my public ip-address.

In that case all is fine and just the check does not perform well - nothing to worry about.