Flutter, тип «int» не является подтипом «string», вызывающего rest API

Проблема в вашем Currencymodel вы пытаетесь добавить строку в int

измените эту строку final int uuid; на эту final String uuid;

как упомянул @OMi Shah, вам нужно удалить int.parse и использовать его вот так uuid: json['data']['uuid'],

если у вас проблема с вашим статусом, то вам нужно разобрать его на int вот так int.parse(json['status']),

• Создайте правильный класс модели из json и попробуйте
• https://itsallwidgets.com/json-to-dart-converter-support-null-safety

бывший:

class CurrencyModel {
  final int? status;
  final List<Data>? data;

  CurrencyModel({
    this.status,
    this.data,
  });

  CurrencyModel.fromJson(Map<String, dynamic> json)
    : status = json['status'] as int?,
      data = (json['data'] as List?)?.map((dynamic e) => Data.fromJson(e as Map<String,dynamic>)).toList();

  Map<String, dynamic> toJson() => {
    'status' : status,
    'data' : data?.map((e) => e.toJson()).toList()
  };
}

class Data {
  final String? uuid;
  final String? displayName;
  final String? displayNameSingular;
  final String? displayIcon;
  final String? largeIcon;
  final String? assetPath;

  Data({
    this.uuid,
    this.displayName,
    this.displayNameSingular,
    this.displayIcon,
    this.largeIcon,
    this.assetPath,
  });

  Data.fromJson(Map<String, dynamic> json)
    : uuid = json['uuid'] as String?,
      displayName = json['displayName'] as String?,
      displayNameSingular = json['displayNameSingular'] as String?,
      displayIcon = json['displayIcon'] as String?,
      largeIcon = json['largeIcon'] as String?,
      assetPath = json['assetPath'] as String?;

  Map<String, dynamic> toJson() => {
    'uuid' : uuid,
    'displayName' : displayName,
    'displayNameSingular' : displayNameSingular,
    'displayIcon' : displayIcon,
    'largeIcon' : largeIcon,
    'assetPath' : assetPath
  };
}

// your code

Map<String, dynamic> json = {
    "status": 200,
    "data": [
      {
        "uuid": "85ad13f7-3d1b-5128-9eb2-7cd8ee0b5741",
        "displayName": "VP",
        "displayNameSingular": "VP",
        "displayIcon":
            "https://media.valorant-api.com/currencies/85ad13f7-3d1b-5128-9eb2-7cd8ee0b5741/displayicon.png",
        "largeIcon":
            "https://media.valorant-api.com/currencies/85ad13f7-3d1b-5128-9eb2-7cd8ee0b5741/largeicon.png",
        "assetPath":
            "ShooterGame/Content/Currencies/Currency_AresPoints_DataAsset"
      },
      {
        "uuid": "85ca954a-41f2-ce94-9b45-8ca3dd39a00d",
        "displayName": "Dough",
        "displayNameSingular": "Dough",
        "displayIcon":
            "https://media.valorant-api.com/currencies/85ca954a-41f2-ce94-9b45-8ca3dd39a00d/displayicon.png",
        "largeIcon":
            "https://media.valorant-api.com/currencies/85ca954a-41f2-ce94-9b45-8ca3dd39a00d/largeicon.png",
        "assetPath": "ShooterGame/Content/Currencies/Currency_Dough_DataAsset"
      }
    ]
  };
    
 CurrencyModel cModel = CurrencyModel.fromJson(
      json); // responseJson (json) - Map<String, dynamic>

  print(cModel.data!.length);


`

Изменять final int uuid; к final String uuid; в модельном классе

Изменять uuid: int.parse(json['data']['uuid']), к uuid: json['data']['uuid']

потому что вы пытаетесь проанализировать поле «uuid» из ответа API как int

class CurrencyModel {
      final int status;
      final String uuid;
      final String displayName;
      final String displayNameSingular;
      final String displayIcon;
      final String largeIcon;
      final String assetPath;
    
      const CurrencyModel({
        required this.status,
        required this.uuid,
        required this.assetPath,
        required this.displayIcon,
        required this.displayName,
        required this.displayNameSingular,
        required this.largeIcon,
      });
    
      factory CurrencyModel.fromJson(Map<String, dynamic> json) {
        return CurrencyModel(
          status: json['status'],
          uuid: json['data']['uuid'],
          assetPath: json['data']['assetPath'], 
          displayIcon: json['data']['displayIcon'], 
          displayName: json['data']['displayName'], 
          displayNameSingular: json['data']['displayNameSingular'], 
          largeIcon: json['data']['largeIcon'],
        );
      }
    }

// To parse this JSON data, do
//
//     final currencyModel = currencyModelFromJson(jsonString);

import 'dart:convert';

CurrencyModel currencyModelFromJson(String str) => CurrencyModel.fromJson(json.decode(str));

String currencyModelToJson(CurrencyModel data) => json.encode(data.toJson());

class CurrencyModel {
    int status;
    List<Datum> data;

    CurrencyModel({
        required this.status,
        required this.data,
    });

    factory CurrencyModel.fromJson(Map<String, dynamic> json) => CurrencyModel(
        status: json["status"],
        data: List<Datum>.from(json["data"].map((x) => Datum.fromJson(x))),
    );

    Map<String, dynamic> toJson() => {
        "status": status,
        "data": List<dynamic>.from(data.map((x) => x.toJson())),
    };
}

class Datum {
    String uuid;
    String displayName;
    String displayNameSingular;
    String displayIcon;
    String largeIcon;
    String assetPath;

    Datum({
        required this.uuid,
        required this.displayName,
        required this.displayNameSingular,
        required this.displayIcon,
        required this.largeIcon,
        required this.assetPath,
    });

    factory Datum.fromJson(Map<String, dynamic> json) => Datum(
        uuid: json["uuid"],
        displayName: json["displayName"],
        displayNameSingular: json["displayNameSingular"],
        displayIcon: json["displayIcon"],
        largeIcon: json["largeIcon"],
        assetPath: json["assetPath"],
    );

    Map<String, dynamic> toJson() => {
        "uuid": uuid,
        "displayName": displayName,
        "displayNameSingular": displayNameSingular,
        "displayIcon": displayIcon,
        "largeIcon": largeIcon,
        "assetPath": assetPath,
    };
}