Adding a Nextcloud CalDAV Account in macOS fails: "Accountname/Password couldn't be verified"

Nextcloud version: I don’t know, where to find the version in the settings
Operating system and version: macOS 14 (Mojave)

The problem:
I cannot add a Nextcloud CalDAV account to macOS.

The steps to reproduce:
https://docs.nextcloud.com/server/13/user_manual/pim/sync_osx.html
I used exactly those steps.

Result:

Surprisingly adding a CalDav account from another Nextcloud Account, that works without problems.
On the same Mac.

Is there any hidden configuration setting to make it work?

I’m not the admin of the both Nextcloud installations, only a user. The admin is new to Nextcloud and had no idea. So I try to help him with posting the problem here, hoping for an advice :slight_smile:
Thanks.

Edit:
I found a related post with the suggestion to use “advanded” mode for adding the account:

It does not work here. I still get the same result.

Is there really no one, who has an idea how to solve the problem?

Is your Nextcloud reachable via https or only via plain http?

Via https.

I also tried to add an CalDAV Account on an iPhone with iOS12. It doesn’t work neither, I get the same result as on the macOS.

The login into the webinterface works fine.

I tried the following method (Posting 4) as well, without success: