For clients that are set up Composer 1X, we offer a Checkout abandonment segment which allows you to target users that have started but did not complete checkout.
In case you're not using this version of Composer, we recommend setting a custom cookie programmatically on the startCheckout event as described here. Once this is done, you can create a user segment for users in Composer who have this cookie set and don’t have access. More information is available under this link.
This way you would be essentially targetting users via an Experience, who started checkout but didn’t complete it.