Return custom response on .NET Core model binding errors

 This example shows how to return a custom IActionResult when the model binding validation fails:

builder.Services.AddControllers().ConfigureApiBehaviorOptions((options) =>
{
    options.InvalidModelStateResponseFactory = (actionContext) =>
    {
        return new BadRequestObjectResult(new
        {
            Error = actionContext.ModelState.First().Value?.Errors.First().ErrorMessage
        }); 
    };
});

then, if you use axios for the API call:

try {
    const result =  await axios.post(`......`, {.....});
} catch (e) {
    console.dir(e.response.data.error);
}