Keep the package subtotal in pence
For one of each selected package, the observed inclusive merchandise arithmetic is 810 pence. A confirmed merchandise-only credit of£8.10 leaves exactly£0.00 merchandise. A credit of£8.11 is above that subtotal and is refused;the tool does not create a negative price or infer that a voucher pays cash back.
Allow the exact full credit
Money is parsed into integer pence with at most two decimal places. Package counts must be whole numbers within the stated limit. This avoids a floating-point comparison rejecting an exact credit. Two user-entered£47.99 packages total£95.98 exactly, and three£0.10 packages total£0.30. These are calculation tests, not current retail offers.
Retain delivery after the credit
A full merchandise credit does not automatically erase shipping or other fees. With£4.99 shipping and£1.25 other actual charge entered, the remaining total is£6.24 if all other charges are explicitly zero. Those are test inputs, not observed grocery fees or proof that a seller accepts a particular credit. Already-included VAT is not added twice.
Reject missing and invalid inputs
Blank charges withhold the full total. Negative values, exponent notation, excess precision and above-limit entries are rejected. The ledger does not validate loyalty discounts, food-contact suitability, stock or checkout. Use an actual confirmed quote and retain the separate fulfilment conditions before treating any result as payable.
A purchase case to keep explicit
A credit note may exclude delivery or apply only to particular merchandise. Enter only a confirmed eligible amount. When a credit exceeds the entered subtotal, the tool refuses it rather than turning the excess into cash back or silently erasing unrelated charges.
Sources & scope
Checked November 5, 2026. Manufacturer and retailer references support the specific statements. Dated displayed prices are not final checkout quotes, performance rankings or performance testing. This shopping reference does not replace the exact product label or retailer instructions. Current received labels and independent materials/food-contact/content/commerce review remain pending.
Tesco GB tie-handle bin liners321788728 ↗
Waitrose Bacofoil medium12 zipper bags824828 ↗
Waitrose non-PVC40mx350mm film480470 ↗
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