This Automation action will add an item to the sales order as a new order row. The SKU can be an inventory managed item or a service item, but if inventory managed then it must be on-hand in the warehouse assigned to the order. The item is added with a zero price for your customer.
When creating a rule to add a free SKU, select the action from the dropdown then enter the Product ID. This ID is visible under the SKU in the Product List or in the URL of the Product page, after 'pID=XXXX'.
Once you've entered a valid Product ID, you can then enter the quantity you want to be added to orders.
This action cannot be applied to an invoiced order and we would recommend ensuring the item is added before the sales order is fulfilled.