First Purchase Incentive below 'Add to Cart'

If your eCommerce store has a first purchase incentive, apply a block outlining the incentive below the ‘Add to Cart’ button with a clear ‘Sign Up’ CTA.
This is less dependent on customers engaging with popups that users tend to close immediately. It also encourages transactions when they matter.

Furthermore, this encourages non-purchasers to join your mailing list.
Enabling emails to drive abandoned purchasers.