There are several different types of items that can be selected when you create or edit a product.

The stock item is the completely ordinary item that is sold.
If you set an item as a composite item, you can add some products in the “Composite products” tab by clicking “+”

When you sell the composite item, each item will be sold as an individual item.
For the bundled item, some products must also be added in the “Composite products” tab
Unlike the composite item, all products linked to the bundled item will be sold as a single package.
The service is not a product that can be deducted from stock.
Want to know more?
Read more in these related articles:
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This quick guide reviews how Sapera's product design works with inheritance from categories, and how you customize individual product settings.