Hide the promo code field behind a link

When to use it

When checkout shows an open 'Promo code' box to every shopper and exits cluster around that step.

How to run it

Collapse it to a plain 'Have a promo code?' link that opens the field inline, and auto-apply eligible discounts where you can.

Why it works

Point every eye at the one action

An empty coupon box tells full-price buyers they're overpaying. In Baymard's testing, shoppers left checkout to hunt for codes on Google, and once they leave, many never return.

Source: Baymard Institute