So the title says it all but I have an annoying bug (?). If I send invites for an event to users out of nextcloud they receive the event and can respond to it. But if they select yes/no/… the status of the invite does not change. I receive a confirmation from their gmail that they accepted the invite.

I use nextcloud on unraid using docker. Mails are being send using iCloud. Nextcloud is using an external domain via Nginx proxy manager and cloudflare.

Tips, ideas where to look?