I am looking for the best practice on the following scenario when utilizing ecommerce transaction (purchase) tracking with GA4:
A customer has gone through the entire checkout flow and added a product to their cart. During checkout they add an optional add on (say it's a warranty or what have you.) When you send over the items array for the purchase event, should only the original product in the cart be sent over for tracking or should there now be two items, one for the product and one for the add on that was added in the cart during checkout? Note that this add on could not be purchased individually and is therefore not a standard product someone could purchase (i.e. they can't buy a warranty without also buying the product but they can buy the product without the warranty.)
Ideally answers will include sources for this best practice.
Some other examples:
- add a t-shirt to your cart and add on gift wrapping
- book a night at a hotel and add on the romance package
- purchase a scuba diving tour and add on an extra scuba tank
Thanks in advance!