freezed_union_key.dart

// OK
@Freezed(unionKey: 'type')
class FlightPlan with _$FlightPlan {
  factory FlightPlan.first({
    required String type,
    required String monitorMaker,
    required bool baggageDeliveryAvailable,
  }) = FirstClassFlightPlan;

  factory FlightPlan.economy({
    required String type,
    required String beefOrChicken,
  }) = EconomyClassFlightPlan;

  factory FlightPlan.fromJson(Map<String, dynamic> json) =>
      _$FlightPlanFromJson(json);
}

// NG
@Freezed(unionKey: 'plan_type')
class FlightPlan with _$FlightPlan {
  factory FlightPlan.first({
    required String planType,
    required String monitorMaker,
    required bool baggageDeliveryAvailable,
  }) = FirstClassFlightPlan;

  factory FlightPlan.economy({
    required String planType,
    required String beefOrChicken,
  }) = EconomyClassFlightPlan;

  factory FlightPlan.fromJson(Map<String, dynamic> json) =>
      _$FlightPlanFromJson(json);
}