Klar already had a popup with a welcome offer they use to grow their email list. When you sign up, you are immediately given a discount code. Klar wanted to remind the visitors who received the discount code but did not proceed to make a purchase, that they still had an unused discount code the next time they returned to the website.
How they did it
They had already created a popup with a welcome offer, so now they only needed to create the discount reminder. They created another popup with a click-to-copy discount code and targeted it to existing subscribers with more than 1 previous visit to the website.