Update selected fields on an existing event. Unlike PUT /events/{eventId}, which requires the complete event object, this endpoint accepts a partial event object and only modifies the fields explicitly provided in the request body. Fields not included in the request remain unchanged. All properties in the request body are optional but at least one must be supplied.

Editability restrictions based on event state:

• Past or cancelled events: only title, description and customAttributes may be updated.
• Active future events: all listed fields may be updated.

Supplying a field that is not allowed for the event's current state will return 400 INVALID_REQUEST_BODY.

type / spaceId / location mutual exclusion:

• For ONLINE events, location must not be supplied; if the event previously had a location it will be cleared.
• For OFFLINE events, spaceId must not be supplied; if the event previously had a spaceId it will be cleared.

Recurring events: the request updates only the single occurrence identified by eventId; there is no way via the public API to apply the change to the whole series or to "this and future" occurrences.