class Destination { final int amount; // transfered as string final String address; final String assetId; Destination( {required this.amount, required this.address, required this.assetId}); factory Destination.fromJson(Map json) => Destination( amount: int.parse(json['amount'] as String), address: json['address'] as String, assetId: json['asset_id'] as String, ); Map toJson() => { "amount": amount.toString(), "address": address, "asset_id": assetId, }; }