How to fix Flutter Expected a value of type 'Map<String, dynamic>', but got one of type 'List<dynamic>'

you can do it like that

MedicalRecordsModel.fromJson(jsonDecode(response.body) as Map<String, dynamic>);

change the getRecord as follows

Future<MedicalRecordsModel> getRecords() async {
    var url = ConstantMedicalRecords.medical_records_api;
    log('$url');
    try {
      final response = await client.get(url);
      if (response.statusCode == 200) {
        return MedicalRecordsModel.fromJson(jsonDecode(response.body)[0]);
        // print(recordsModel);
      }
    } catch (Exception) {
      print(Exception);
      print("Error occured");
    }
  }

I think jsonDecode gives list of Maps therefore your json map is the first element of that list.

This code wiil work as you expected:

import 'package:json_helpers/json_helpers.dart';

void main() {
  // responseBody is the same response.body

  // When response is a list of objects
  final list = responseBody1.jsonList((e) => MedicalRecordsModel.fromJson(e));
  var obj = list[0];
  print(obj.category);
  print(obj.fileName);

  // When response is an object
  obj = responseBody2.json((e) => MedicalRecordsModel.fromJson(e));
  print(obj.category);
  print(obj.fileName);
}

final responseBody1 = '''
[
   {
      "id":"103",
      "category":"DOCUMENT",
      "fileName":"Check Up",
      "dateTimestamp":"2021-02-1012:59:46",
      "description":"string",
      "upload":"String",
      "patientName":"1",
      "age":"25",
      "address":"Earth",
      "userId":null,
      "patientId":12,
      "isActive":true
   }
]''';

final responseBody2 = '''
{
   "id":"103",
   "category":"DOCUMENT",
   "fileName":"Check Up",
   "dateTimestamp":"2021-02-1012:59:46",
   "description":"string",
   "upload":"String",
   "patientName":"1",
   "age":"25",
   "address":"Earth",
   "userId":null,
   "patientId":12,
   "isActive":true
}''';

class MedicalRecordsModel {
  final String id;

  final String category;
  final String fileName;
  final String dateTimestamp;
  final String description;
  final String upload;
  final String patientName;
  final String age;
  final String address;
  final dynamic userId;
  final int patientId;
  final bool isActive;
  MedicalRecordsModel({
    this.id,
    this.category,
    this.fileName,
    this.dateTimestamp,
    this.description,
    this.upload,
    this.patientName,
    this.age,
    this.address,
    this.userId,
    this.patientId,
    this.isActive,
  });

  factory MedicalRecordsModel.fromJson(Map<String, dynamic> json) {
    return MedicalRecordsModel(
      id: json['id'] as String,
      category: json['category'] as String,
      fileName: json['fileName'] as String,
      dateTimestamp: json['dateTimestamp'] as String,
      description: json['description'] as String,
      upload: json['upload'] as String,
      patientName: json['patientName'] as String,
      age: json['age'] as String,
      address: json['address'] as String,
      userId: json['userId'] as String,
      patientId: json['patientId'] as int,
      isActive: json['isActive'] as bool,
    );
  }
}

Output:

DOCUMENT
Check Up
DOCUMENT
Check Up

That is, when response is a list of objects:

final list = response.body.jsonList((e) => MedicalRecordsModel.fromJson(e));

When response is an object:

final object = response.body.json((e) => MedicalRecordsModel.fromJson(e));

If you don't know what the result is, then you can try both methods.

response.body.json((e) => Model.fromJson(e));
response.body.jsonList((e) => Model.fromJson(e));

If you have already decoded a JSON string and want to convert the result (or part of it), you can use the following methods:

If the type of the decoded value is Map:

final object = value.json((e) => Model.fromJson(e));

If the type of the decoded value is List:

final objects = value.json((e) => Model.fromJson(e));

Every response is sended and received as text, which can be converted to the
Map Format with the dart inbuilt core library import 'dart:convert';.

So the response from the request can be treated like this.

final res = await http.post(Uri.parse(url),  body: json.encode({
          'userId': uid,
          'email': email,
        }),
        head body: json.encode({
          'userId': uid,
          'email': email,
        }),
        headers: {'Content-Type': 'application/json', 'token64': token});

here json.encode() is used to convert to String from Map.

now res variable contain the response which is also a string which can be convert to the Map with json.decode() like this.

final data = json.decode(res);

when working with the data sometimes we occur errors like Map is not a type of Map<String, String> etc.

Which can be solved by type casting the res, like this.

Map<String, String> notification = Map<String, String>.from(data['notification']);

I see these type casting method used in the The boring Flutter Development show in Youtube.