What is Attach rate?
Attach rate is the share of orders that include a specific add-on, such as a free gift, an upsell or a bundle. If 120 of 1,000 orders carry the add-on, the attach rate is 12 percent.
Measure it per offer and per period. A falling attach rate on a stable offer usually means the offer is shown less often or placed less visibly, not that shoppers changed their minds.