Why is asuscomm DDNS not working?

Question

ASUS

created a name on ddns asuscomm.com . but its ip is not the same as my
router says The
wireless router uses a private WAN IP address. This router is in a NAT environment and the DDNS service cannot work.
My external ip found out on 2ip.ru shows 87.244.186.167 , it matches the WAN address that is indicated on the router
. Why does not it work?
we also have such a thing set up vpn on the router, I don’t know exactly how it was done, I set up a friend, the asus RT-N12+ router model
ps the goal is to use RDP on several PCs in general