Yes! Your subscribers can easily add a product to their existing subscription order.
From the Ongoing Subscriber Portal ➡ Click Add Product
Select the product ➡ Click Save
No checkout or credit card needed - the new total price of your order is automatically adjusted.
This item will be added as a subscription to your existing subscription order.
Changes will be applied to your upcoming subscription order.
You can always remove the item later if you wish, by clicking Remove.