Repeating / recurring purchase is something that you buy on a regular basis. For example you might be buying milk every week. If this is the case then you can make it a recurring expiry.
You can setup item repetitions from "Edit Storage Details" for the item. Tap on the item row (anywhere on the right side of the row except the + or list icon) to bring up the edit screen. Now to setup repetitions you have to first setup item expiry. Pick an expiry date and go back to the edit screen. Now go down to the "Repetition section" and tap on "Repetition" row. Enable "Auto repeat shopping". Pick a repetition period from the slider: whether the item is a daily, weekly, monthly or yearly.
Also pick when a repetition period should begin? There are a couple of options to choose from :
After Expiry : This is good for regular interval purchases. For example, say today is Tuesday & you regularly do weekly purchases of milk on Saturdays. So set expiry date as next Saturday and set repetition to every 1 week so that the item will automatically get added to the list every Saturday.
After Shopping Completed : This is a good repetition option if you have items that have a fixed shelf life. For example say ketchup or medicines. In this case just set the expiry date as you see on the product label and once the item expires the item will get auto added to list. The next expiry date will only begin after you purchase the item and checkout from the shopping list.