Use Revise Order to add products to an order that's already paid. For example, the customer calls to add a bottle before you send it. You can charge the customer the extra, or give it to them free.
How to add products and charge the difference
Go to Orders and click the order number to open the order panel.
Click Revise Order.
Click Add more products and add the products, or click + on a product that's already in the order.
The Order Summary shows the extra under Additional payments.
Under Additional Payments, choose how the customer is paying:
Card: charge the customer's saved card, or click Add New Card.
Cash: enter the amount paid in cash.
Check Balance due is $0.00.
Click Pay & Submit Revision, then OK.
How to add products for free
In Revise Order, add the products.
In Additional Discount, enter the extra amount. The Order Summary shows the amount as Custom discount.
Check Balance due is $0.00. The button changes back to Submit Revision.
Click Submit Revision, then OK.
What happens next
WithWine creates a new order linked to the original. If Adjust Stock Movements is on, the added products are taken out of stock. If Send Receipt Email is on, the customer gets a new receipt. See "How to revise an order".