Field name `items` is not valid for model `CartItem`

I have set a related name in my model . then I have declare this on my serializer . But I got in error

This is my

class CartItem(models.Model):
    cart = models.ForeignKey(
        Cart, on_delete=models.CASCADE, related_name='items')
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    quantity = models.PositiveSmallIntegerField(

    class Meta:
        unique_together = [['cart', 'product']]

and this is my

class CartSerializer(serializers.ModelSerializer):
    id = serializers.UUIDField(read_only=True)

    class Meta:
        model = CartItem
        fields = ['id', 'items']

got this error when accessing

on my cart

my error screen shot