Inventory "Variant" doesn't work

Inventory variant doesn't work for some IDs (eg 1866)

Get Request Method : https://www.headout.com/api/public/v1/inventory/list-by/variant?variantId=1866&startDateTime=2019-07-28T00:00:00&limit=100&offset=0&limit=10

Response:
{
    "error": {
        "code": "CAL-0121",
        "title": "Itinerary error",
        "message": "This tour is not available anymore."
    }
}