#1662 Response status code does not indicate success: '403' ('Forbidden')

[Daniel]

The following error is reported to me for one of the calendars:
Response status code does not indicate success: '403' ('Forbidden')

Unfortunately, the error message does not, as usual, contain an indication of which event this concerns. The user has received and accepted several appointment invitations. I see other entries from him. Other devices can easily be synchronized via CalDAV, the problem only occurs with Outlook.

Windows 10 20H2
Outlook 365 Version 2109 Build 14430.20298
CalDav Synchronizer 4.1.0.0
SOGo 5.2.0
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