Use an offer at checkout

The client at the till says there's a special this month, and they're right. Discounts here aren't a number you type — they're offers a manager has already set up, with the fine print built in. Your job is two presses; the till does the arithmetic and enforces the terms.

Putting one on the bill

Next to it, Auto-apply offers is one press that checks every automatic offer against this sale and gives each line whichever qualifying offer discounts it most. If nothing qualifies, nothing happens — it's a check, not a promise.

When it says no

Pick an offer the sale doesn't qualify for and the till refuses loudly, with the actual reason above the total: "Offer is for first-time clients only", "Sale is below the offer minimum", "Offer is not available today", "Offer can be used only once per client", "Offer has reached its redemption limit", or — when the right items aren't on the bill — "This offer has no eligible items on the sale". A smaller line underneath spells out what would make it apply.

That message is the fine print working, not the till failing. Reading it to the client — "this one's for first visits" — is a better conversation than apologising for software that's doing exactly what the promotion said.

Two rules explain almost every refusal that isn't on that list. One discount per line: a line that already has an offer, a manual discount or a changed price is skipped, which is why "no eligible items" sometimes means "you already discounted everything". And one whole-sale discount per sale — a second one is refused rather than quietly stacked.

The code they typed when they booked

Online booking has a Promo code field, checked as the client types it — an invalid or exhausted code is refused before they can book, so nobody arrives holding a code that was never real. A valid code rides along on the appointment, and the moment you press Check out, the discount lands on the cart by itself — provided the sale still qualifies. When it no longer does, the checkout opens without it rather than blocking you; pick the offer manually if you want the till to say why.