POST method returning 400 bad request after adding a new param to the RequestBody

I added a new object parameter to the RequestBody of POST method. Below is the syntax of the method at controller:

public void registerTask(@RequestBody MyRequestDto myRequestDto)updated MyRequestDto class:private final String existing1;private final String existing2;private final NewParam myNewparam; // this is the new param that is added

the initialization is done through constructor:

public MyRequestDto(String existing1, String existing2, NewParam myNewparam){this.existing1 = existing1;this.existing2 = existing2;this.myNewparam = myNewparam;}

This is the new Param class definition:

public class NewParam {    private final String name;    public NewParam(String name) {        this.name = name;    }    public String getName() {        return name;    }

The issue is when I send the tests through Postman by adding this NewParam, I get 400 bad request. Following are the scenarios and the result:

1. When the NewParam is not added to the request body. result- 201 is returned
2. When the NewParam is added, but the value is set as null. Result - 201 is returned.example:

   {"existing1": "test1","existing2": "test2","myNewparam": null}

3. When the NewParam is added, and initialized to some value. result- 400 Bad Request (The request cannot be fulfilled due to bad syntax)example:

   {"existing1": "test1","existing2": "test2","myNewparam": {"name": "theme"  }}

Note: the integration tests are also failing. While debugging the integration tests, the control is not going to controller, and only getting error as 400 Bad request.