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 $X to get product Y cheaper.
As for the pop up at the checkout page, it can be customized only if you are on the Shopify Plus plan if I am not mistaken.
Hi all, I'm Neomi from Rise.ai app. We have a great solution for your store! With Rise you can create many types of workflows, for example, buy 100$ and get 10% back, or if the cart has 3 items give 10$ back.
in addition, you can apply your workflow on a specific collection at your store.
feel free to contact me at firstname.lastname@example.org