def serialize_event(payload) -> dict:
    """Upstream calendar event -> the fields the interview row stores."""
    if not isinstance(payload,dict):
        payload={}
    online=payload.get("onlineMeeting") or payload.get("online_meeting") or {}
    if not isinstance(online,dict):
        online={}
    start=payload.get("start")
    end=payload.get("end")
    if isinstance(start,dict):
        start=start.get("dateTime") or start.get("date_time")
    if isinstance(end,dict):
        end=end.get("dateTime") or end.get("date_time")
    if hasattr(start,"isoformat"):
        start=start.isoformat()
    if hasattr(end,"isoformat"):
        end=end.isoformat()
    event_id=payload.get("id")
    return {
        "id": str(event_id) if event_id is not None else None,
        "web_link": payload.get("webLink") or payload.get("web_link") or None,
        "online_meeting_url": (
            payload.get("onlineMeetingUrl")
            or payload.get("online_meeting_url")
            or online.get("joinUrl")
            or online.get("join_url")
            or None
        ),
        "subject": payload.get("subject"),
        "start": start,
        "end": end,
    }