No tasks synced with Mailbox CalDAV service (mailbox.org)

[tqcharm]

Description
No tasks are synced when setting up CalDAV sync with Mailbox service (mailbox.org). However, the connection is established, given that task lists (Projects in Planify) are being synced.

To Reproduce

1. Make sure you have an active Mailbox account.
2. Create tasks in Mailbox's web interface.
3. Set up CalDAV synchronization with your Mailbox account.
4. Check synchronization in Planify with Mailbox tasks.
5. Create tasks in the Mailbox account area in Planify.
6. Check that tasks created locally are snyced with Mailbox.

Expected behavior
Both tasks created in Mailbox's web interface, as well as tasks created in Planify are being synced on both ends.

Actual behavior
No tasks are synced from Mailbox service (from server to local). Tasks created locally (from local to server) are being synced.

Desktop (please complete the following information):

• OS or DE: Fedora Silverblue 43 with GNOME 49
• Planify Version: 4.15.2 (Flatpak from Flathub).

[themagiulio]

I was about to report the same issue. When I set up CalDAV synchronization with my Mailbox account, I cannot see previously added task, however, I can add tasks that I can then see on Mailbox's web interface. If I try to complete a task an error occurs with the following message:

PUT https://dav.mailbox.org/caldav/MzM//<SOME-IDENTIFIER>.ics failed: HTTP 201 Created

If needed, I could provide other details you may need to debug.

[tqcharm]

I have somehow overlooked that tasks created in Planify are actually synced to the Mailbox server (it's only those on Mailbox's account that are not synced locally). I have updated the issue description. Thanks for the hint @themagiulio .