As per your concern, Growave can satisfy your needs with discounts.
It can be set as a campaign from our Social Sharing product or can be delivered even better from our Loyalty and Rewards program, where you can let users who buy X get Y discount and spend more than $X to get product Y cheaper.
As for the pop up at the checkout page, it can be customized only if you are on the Shopify Plus plan if I am not mistaken.
|2 hours ago|
|3 hours ago|