Well, I logged in into my account. Then I searched for the WebDAV address. When I tried to connect via WebDAV, it didn’t work (code 503) and I was logged out in my Browser. When I tried to log back in in the browser, I got the massage, that my account would be deactivated as u see at the screenshot.
Tab Digital is a “sign up” provider, so they probably use the Preferred providers app. The Preferred providers app sends an email for confirmation. If you do not confirm your e-mail address within 6 hours, the account will be deactivated (this is how the app works). The account can then only be activated via support of the Nextcloud provider.