Invalid object error in EF

I want to get product and all its images. but i am getting invalid object error

 [HttpGet("prodimages")]
        public IActionResult ProductWithImages(int PID=2)
        {
            var productsWithImages = _context.Product.Where(p => p.Id == PID)
                .Include(p => p.Images).ToList();
            return Ok(new { status = "200", product = productsWithImages, gender = "M" });
        }

 public class Product
    {
        public int Id { get; set; }

        public string Name { get; set; }
        public ICollection<ProductImage> Images { get; set; }
     }

 public class ProductImage
    {
        public int Id { get; set; }

        public string ImageName { get; set; }
        public string ImageSize { get; set; }
        public int ProductId { get; set; }
        public Product Product { get; set; }
    }

I am getting error "Invalide object ProductImage"

Do i need to create some relationship?