Flutter sends a post request with parameters through dio

I wanted to pass a parameter of type json, but found it was always wrong, so I thought about adding application/json to the header, and tried many times without success. Halfway through, I saw that the default data request type is application/json. But subconsciously ignore it and continue to look for solutions in the wrong direction.
Later, I thought that there might be a problem with the writing of the post method, and it was successfully resolved after searching.

I was so angry at my own stupidity, hey, when encountering a problem, you should first think about whether the direction of solving the problem is correct, and then read more official documents.

Error instance:

      Dio dio = new Dio();
      response = await dio.post(
          'URL',
      queryParameters: {
    
    
        "name": "xiaoming",
        "age": "18",
      });
      print(response);

Correct example 1:
document:

response=await dio.post("/test",data:{
    
    "id":12,"name":"wendu"})

Correct example application 2:

      Dio dio = new Dio();
      response = await dio.post(
          'URL',
      data: {
    
    
        "name": "xiaoming",
        "age": "18",
      });
      print(response);

Correct example 3:

      Dio dio = new Dio();
    ///创建Map 封装参数
    Map<String,dynamic> map = Map();
    map['name']='xiaoming';
    map['age']='18';
      response = await dio.post(
           'URL',
          data: map,
  );
      print(response);