Hey there,
I’m pretty new to Nextcloud and self-hosting, but I’d like to share an issue I ran into when installing the Nextcloud app on my iPhone. I couldn’t find a solution for it in this forum or elsewhere, but I suspect others like me might encounter the same problem.
My domain and my Nextcloud instance run locally only. When I’m on the go, I access it via VPN.
Many services require a valid SSL certificate, so I followed this guide to set up a Let’s Encrypt certificate and register a domain (let’s call it mydomain.dedyn.io). The setup worked fine for me, with a few minor tweaks. I’m using Nginx Proxy Manager as my reverse proxy, and Pi-hole handles my local DNS records, pointing to my Nginx Proxy Manager. Nextcloud is running, apps are installed, and everything was working well.
Things got weird when I tried to use the Nextcloud iOS app. I already had other apps where I could log in with my FQDN (like “service.mydomain.dedyn.io”) and credentials, but unfortunately, the Nextcloud app was a different story. I couldn’t log in with my FQDN at all, and I had no idea why. I tweaked the Nextcloud config according to its documentation, as well as the NPM config, and consulted ChatGPT for potential issues, but nothing changed. I still couldn’t log in via the app, although I could use the FQDN in Safari. (Weirdly, trying to log in to the app and then immediately using Safari to log in also failed, probably due to some cache/cookie issue.) However, using my local IP address worked, but that isn’t desirable because it causes other issues.
In the end, ChatGPT suggested using an iPhone app to run pings and DNS checks for further troubleshooting.
I installed Net Analyzer from the App Store (it’s free, with some minor ads) and it did the job. When I checked the DNS entries for my FQDN, I was surprised to see the (fake) entry I had added at dedyn.io. My DNS server for the local network is set to my Pi-hole and nothing else—no private relay or VPN—so I wondered why that record was showing up. I suspected that might be the problem…and I was right.
After deleting the entry, waiting about 10 minutes, and restarting my iPhone, I was finally able to log in to my Nextcloud with the FQDN and credentials. Strangely, I’ve had similar issues with other apps too, and after removing the fake record, those issues went away. So I suppose this is not a Nextcloud only issue.
So what’s my point? I realize this may have been a newbie mistake—forgetting to delete that fake A record—but there are probably others who want to get started with Nextcloud or other open source projects but aren’t very experienced (like me, haha).
I assumed pointing Pi-hole to the right record would be enough, and it mostly was—until it turned out not to be, thanks to Big Apple. 
Anyway, I just wanted to share this so others might avoid similar problems or at least solve them more quickly. And yes, Nextcloud is a great project and this forum is fantastic! Thanks for all the help I’ve received here already!