Hint for NC and iOS reminders app users

I just want to share one thing I recently learned and did not see this anywhere in the documentation for NC:

I run NC on a Raspi at home and use it store calendar, contacts (and reminders).
I connected an iOS device to it. I have a dynamic IP domain (no-ip) and for this domain I use a lets encrypt certificate.

What worked without issues:
I connected the NC iOS app to my NC by directing it to use the local IP address “192.168.xxx.xxx.”
I created two “app passwords” in NC, then I created a “profile” from within the iOS NC app, then imported the profile and manually eneterd the app passwords.
From there on via CardDAV and CalDAV the calendar and contacts did synchronize nicely. The NC app ran nicely as well.

What did not work:
The reminders app did not sync in any way with NC.

I recently reinstalled the iOS NC app and there I did not use the local IP address but I used the dynamic domain address. Suddenly it all worked right away.

So it seems to me that Apple for some weird reasons only allows reminders to sync if the source uses a proper encryption certificate and this matches the server name. To be clear: the “weird” part is not this security check. It is a) that when failing the check we do not get any error messages and b) while reminders are handled this way, both contacts and calendars do not care.

Tip for other users: Connect the app via a domain with certificate. Don’t use a local IP.

Thanks for the hint. But I think the real problem is the use of the local IP address. If a Nextcloud can also be accessed via a dynamic address, this standardised name should always be used for all access. Even if the dynamic address is used, there is no access to the Internet from the inside.