ASP.NET Core 8 Web API data validation ignores data annotations

Question

I'm trying to get automatic data validation working in an ApiController but when the user sends incorrect/missing data a JSON deserialization failed error message is returned instead of the custom ErrorMessage.

ProfilesController.cs

using ClassLibrary.Models;
using ClassLibrary.Services;
using Microsoft.AspNetCore.Mvc;
using Swashbuckle.AspNetCore.Annotations;
using ClassLibrary.Models.API.Responses.Profiles;
using ClassLibrary.Models.API.Requests;
using Microsoft.AspNetCore.Authorization;

namespace API.Controllers
{
    [ApiController]
    [Route("v1/[controller]")]
    public class ProfilesController : Controller
    {
        private IProfileManager _profileManager;

        public ProfilesController(IProfileManager profileManager)
        {
            _profileManager = profileManager;
        }

        [Authorize]
        [HttpPatch("about")]
        public async Task<IActionResult> UpdateAbout([FromBody] UpdateAboutPayload payload)
        {
            await _profileManager.UpdateAboutAsync(payload.About);

            return Ok();
        }
    }
}

UpdateAboutPayload.cs

using System.ComponentModel.DataAnnotations;

namespace ClassLibrary.Models.API.Requests
{
    public class UpdateAboutPayload
    {
        [Required(ErrorMessage = "About is required")]
        [StringLength(500, ErrorMessage = "About must be between 0 and 500 characters long")]
        public required string About { get; set; }
    }
}

When I send the following data

{}

I get this error

{
  "type": "https://tools.ietf.org/html/rfc9110#section-15.5.1",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "errors": {
    "$": [
      "JSON deserialization for type 'ClassLibrary.Models.API.Requests.UpdateAboutPayload' was missing required properties, including the following: about"
    ],
    "payload": [
      "The payload field is required."
    ]
  },
  "traceId": "00-402c938fa2cb172de6a89b521f8fcae1-88ebfe9d6c674e35-00"
}

instead of the error message configured in the [Required] attribute

Answer 1

The issue was caused by the required modifier on the About property, removing it solved the error.