You can attach a loyalty program to an analysis group. This will allow you to sell a group of items, for example, tins of cat/dog food, and allow the loyalty scheme to accumulate for the total of the items sold in that analysis group.
To set up a loyalty scheme on an analysis group
Go to: Stock menu > Analysis Groups.
Enter a Qty Threshold amount and a Free Qty amount.
In the example below, when a client buys 10 stock items from the Hills analysis group, they will be entitled to a free one.