Field Notes · 12 March 2026
Why voucher double-fires flatten a Sunday flash
When the same code applies twice in checkout, conversion charts lie — and teams blame the wrong channel.
A Midlands fashion client watched Sunday conversion dip despite strong email opens. The Tracking Health Check found the weekend voucher attached once in the cart and again at payment confirmation.
That second fire inflated “discount applied” counts while paid orders stayed flat. Marketing thought creative fatigue was the culprit; merchandising thought sizing was wrong.
What to inspect before the next drop
- Does the coupon parameter appear on both
add_to_cartandpurchaseevents? - Does the till export show one redemption per order ID?
- On mobile Safari, does a refreshed checkout page re-apply the code silently?
If any answer is fuzzy, freeze the stackable rule for the public window and keep early-access codes single-use. Your flash-sale conversion story becomes readable again — even if the headline rate looks quieter.