External URL issues internally via IOS

Hi all, I’m running NextCloud in a TrueNAS Scale docker with NGINX Proxy Manager forwarding the external IP internally.

Currently I can access the DuckDNS URL from my laptop on the internal network. I can access the URL externally from my iPhone and the Nextcloud IOS app, but I cannot access the DuckDNS URL from the internal nextwork on the IOS device.

What is stumping me is that I can access the DuckDNS on the internal network with my laptop, but not my iPhone or NextCloud IOS app.

Any suggestions or pointers on somewhere to start?