https://tools.ietf.org/html/rfc7807 custom ApiBehaviorOptions

gistfile1.txt

services.Configure<ApiBehaviorOptions>(options =>
{
  options.InvalidModelStateResponseFactory = actionContext =>
  {
    var problemDetails = new ValidationProblemDetails
    {
      Detail = "For big problem!",
      Title = "Get a big localized solution!",
    };
    return new BadRequestObjectResult(problemDetails);
  };
});