DDNS problem RT-AX88U - public/private IP

[mobileineurope]

I get the massage “The wireless router currently uses a private WAN IP address” - I do understand that I would get this if I used double-NAT etc., but the problem is that I don’t?
I get a perfectly fine public IP from my ISP in the range 100.109.x.x, which I assume should be fine. Nevertheless, under WAN->DDNS under server certificate it shows me that my certificate is issued to “192.168.1.5” which is the local IP of my router?. Iplookup on my ddns-name shows correct public IP - so from that side everything looks fine.
I’m on Merlin 384.19. I recently changed ISP and I’m unsure if this has been working ever since that. I discovered this just now when my VPN connection from outside to the router failed to work. I run directly through a fiber modem - I run internet through vlan 13 , manual setup on LAN- IPTV.
Why do I get a message about private IP when it clearly is public?

 

[octopus]

I get a perfectly fine public IP from my ISP in the range 100.109.x.x,
That is CGNAT ip-number then you cant reach your VPN-Server from wan-side. Check if ISP can provide a real public ip-number.

 

[mobileineurope]

I get a perfectly fine public IP from my ISP in the range 100.109.x.x,
That is CGNAT ip-number then you cant reach your VPN-Server from wan-side. Check if ISP can privide a real public ip-number.

Thanks - I will try to talk to the ISP.