Add-on purchases are ideal for purchases that you can add to specific products and sub-product offerings.

For example, if you'd like to ensure that a mandatory fee is paid by a person and set a trigger for that fee to be paid only once per year or once per order, add-ons are ideal.

Using the example above, to create a mandatory annual membership fee, here's how:

1. Go to the Options page under the Storefront tab
2. Scroll down to Add-ons
3. Enter "Annual Membership" under Add-On Name
4. Enter the amount
5. Select the Trigger , charged once per person, per year
6. Below the trigger dropdown, you'll see all your products and sub-product offerings. You'll want to determine which of the sub-product offerings you'll want this Add-on to apply to.