This article explains how to set up an "Add Free Product" promotion, which automatically adds a complimentary item to any order that meets your criteria.
After selecting the "Add Free Product" promotion type, you can configure the following details:
Available to order on: Select the days when the promotion is active.
Available to order for: Choose the days when the order must be scheduled for pickup or delivery to qualify for the promotion. For example, if you want to add a free cookie to every order scheduled for a Friday, you would select "Friday" here.
After setting your criteria, you will select the product to be added for free. When this product is added to a customer's order through this promotion, its price will automatically be set to 0 in their cart.
Note: The product you select for this promotion will still be available for purchase in your regular product catalog.