POST - https://v2.api-community-tu.org/api/groupmember
Updates or Add an existing Group Member.
{ "Id": 1, "GroupId": 1, "ContactId": 1234, "DateFrom": "2026-06-06T00:00:00+01:00", "DateTo": null, "OfficeId": 2, "StatusId": 3, "Reason": ""}