Missing coupon id
Admin checkout-coupon update/delete ran with an empty [id] (400 Missing coupon id.).
Why this happens
Broken admin link or client called the API without an id. Distinct from Coupon not found (id present, row missing).
Diagnose and fix
1. Open the coupon from the coupons list (do not craft URLs by hand).
2. Hard refresh the admin Payment/coupons UI.
3. If the coupon was deleted, recreate it.
4. Member apply flows use codes, not ids — see coupon-invalid articles.