iOS "protocol error"

I asked a colleague with an iPhone to open the website in Safari, he also could not connect.

SSL is provided via a LetsEncrypt certificate. Do I have to provide a certain protocol in order to allow iOS devices to connect?

Does anyone have a nextcloud instance running, with SSL, which works with iOS devices?


Update:

Maybe it also helps to provide info which apps/sync are working in iOS.
Working:

  • Caldav/Carddav sync for calendar and contacts, configuration in the iOS settings.

Not working:

  • Opening URL in Safari or Firefox on (two) iPhones (all other platforms can open the URL in a browser).
  • Connecting the nextcloud app (error message regarding protocol).
  • Connecting the nextcloud Talk app (no error message, just loading forever). (Works on my Android phone like a charm.)