ModelStateDictionary alternative

Question

I'm trying to build an alternative of ModelState as when I return this from api like return BadRequest(ModelState) it doesn't have much information other than somethings gone wrong with the request. So I have decided to build an alternative which will eventually look like this:

{
   "code": 1000,
   "message": "Invalid request",
   "fields": [
     {
        "name": "Password",
        "message": "Password does not meet complexity requirements."
     }
    ]
}

In order to accomplish this, I have the following models in my api project:

ErrorResponse.cs:

public class ErrorResponse
{
   public string Code { get; set; }
   public string Message { get; set; }
   public Dictionary<string, Field> Fields { get; set; }
}

Field.cs:

public class Field
{
   public string Name { get; set; }
   public string Message { get; set; }
}

Thanks to using FluentResults I can determine the error from the service layer within my controller like so:

if (result.HasError<PasswordError>()) 
{

}

However I've realised that I now need to return the ErrorResponse but each Field has a name and the only way to know the name of the field is through the controller using:

nameof(RegisterRequest.Password)

Is there a way to do this in a clean generic way without using magic strings?