NextDNS and Airport Extreme Configuration

Hi. 

I'm looking for advice on setting up my Airport Extreme with NextDNS. 

First I added my NextDNS IP4 and IP6 in my Airport utility. 

Second I created an account at Dynu for my Airport IP. 

Third I added my Dynu host name into my NextDNS account, but obviously it didn't work "For security reasons, when adding a Dynamic DNS the IP address returned by
the DNS hostname should be the same as your current IP address."

Because my iPad can't have the same IP than my router how can I solve my problem. 

Thanks