public async Task <IActionResult> AddCustomer([FromBody] CustomerDTO dto)
        {
            if (dto == null ||
                string.IsNullOrWhiteSpace(dto.FirstName) ||
                string.IsNullOrWhiteSpace(dto.LastName) ||
                string.IsNullOrWhiteSpace(dto.BirthDate))
            {
                var errorMessage = dto.CreateErrorMessage();
                return(BadRequest(errorMessage));
            }
            if (!DateTime.TryParse(dto.BirthDate, out var dt))
            {
                return(BadRequest("invalid birth date"));
            }

            await Model.AddCustomerAsync(dto);

            return(StatusCode(201));
        }