How to link Linode IP with NextDNS

Hey everyone, I am currently trying to use nextDNS with pihole on a linode. I have completed this guide: https://itproexpert.com/nextdns-pi-hole-setup-doh-secure-dns-over-https/ However nextdns still says im not using it. A person from discord told me this is because nextdns wants to link my public IP instead of the linode's public IP. I want to know how I can do this.
 

Thanks for the help.