TrainAvailabilityRequest

{
    "shoppingId": "train_shop_01J2X9D8Q1",
    "journeyId": "train_journey_G1_20260720",
    "returnJourneyId": "train_journey_G2_20260725",
    "passengerCountByType": {
        "adult": 1,
        "child": 1
    },
    "seatId": "erdengzuo"
}