contact_uuid or contact_external_id (422 contact_required otherwise). Without a stage the opportunity starts in the first open stage; it must be an open stage.{
"group_uuid": "0f0cbec3-10f0-4b21-b1da-6d6437d7f648",
"stage_uuid": "d9f6a2be-a488-46fa-971a-191496f4acf0",
"stage_external_id": "string",
"contact_uuid": "ef88867c-78a0-4c23-93c5-269f718bc3e8",
"contact_external_id": "string",
"title": "string",
"value_cents": 0,
"due_at": "string",
"notes": "string",
"external_id": "string",
"assigned_user_external_id": "string",
"assigned_user_email": "user@example.com"
}