How to convert json Nested String into json in dart flutter

I want to convert nested json string into json
how could i do this

{2022: {Apr: 100.0}} // this is my string
I/flutter ( 7168): Error FormatException: Unexpected character (at character 2)// here error comes out
I/flutter ( 7168): {2022: {Apr: 100.0}}

jsonDecoder("jsonstring here")// I used this code

>Solution :

First encode String then decode it

import 'dart:convert';

void main() {
 String i = "{2022: {Apr: 100.0}}";
 var i2 =  json.decode(json.encode(i));
  print(i2);
}