Coupon could not be applied
Checkout could not apply the coupon (premium.couponApplyFailed). Often a client fallback when apply fails without the more specific Coupon code is not valid.
Why this happens
Transient API/network issue, race, or server rejection mapped to this softer string. Retry may succeed; invalid codes usually show “not valid.”
Diagnose and fix
1. Retry apply; hard refresh if needed.
2. If it keeps failing, treat as Coupon code is not valid and verify admin coupon rules.
3. Check connection (Could not reach the server…).
4. Proceed without coupon if the promo is optional.