Combine offers and upsells as one transaction

Please note: This method will require an experienced web developer

Rather than firing Import Order when the customer submits the checkout page, you will hold that information in the session through out the upsell funnel and pass in the info after the last upsell page. As long as your upsell products have the 'use offer mid' option turn on, all products imported in will be ran on the same transaction.

If the customer tries to navigate away from the site during the upsell funnel you will implement a exit-pop (typically using it with the onbeforeunload function) which you would want to trigger the Import Order with the populated info from the session.

If the customer is in the upsell funnel for an extended amount of time you can make it so the session will close after x amount of time and pass in all the acquired info on Import Order.

https://developer.mozilla.org/en-US/docs/Web/API/WindowEventHandlers/onbeforeunload