Understanding the Structure of the Upsell Flow
The upsell flow has the following elements:

(i) A trigger that defines when to start the flow and for which product. The trigger for this flow is order confirmation. The flow can be triggered for a specific variant of the product or the entire product (including all the variants).
(ii) A time delay that can be defined by you.
(iii) A message that will be triggered after the time delay, which will consist the details of the product you are upselling and a Buy Now button that will take the customer to the checkout page of this product.