If you wish to provide two or more items to a customer in one sale, it is possible to set up bundles. Bundles are product formats that trigger the addition of a combination of items to an order.
Bundles have the advantage over Auto-credit that they are aware of the stock levels of the items in the bundle. The bundle takes the stock level of the lowest stocked item in the bundle and so will go out of stock if any item in the bundle sells out.
Bundles are linked to single pools of stock, so you can have a t-shirt and vinyl bundle, and each t-shirt size (product format) is linked to one stock amount of vinyl.
Auto-credit rules allow the automatic addition of an item to customers orders when a particular product is purchased.
It should be noted that this is not a sale and the Auto-credit function should be used for example to credit the digital version of a physical product that has been sold, or adding an additional promo item to an order.
In order to set up an auto-credit on a particular Product Format go to Format Page > Actions > Set-up Auto-credit
Then choose which format you would like to auto-credit. You can also choose a format from a different product (in the case of a sticker / other promo item for example)