Error 18540 — Promotional pricing error

Your sale_price, lightning deal, or promotional price has a configuration issue — invalid date range, sale price not below standard price, or conflicting promotion overlap.

Amazon validates promotional pricing against several rules: sale must be below standard, dates must be future-valid, multiple overlapping promotions on the same SKU cause conflicts.

1. Set sale_price strictly below standard_price (typically at least 5% lower).
2. Use sale_price_effective_date with a valid 'start_date/end_date' format, e.g., '2026-05-15T00:00:00-05:00/2026-05-22T23:59:59-05:00'.
3. Cancel any conflicting overlapping promotions in Seller Central → Advertising → Promotions before submitting a new one.
4. Don't set sale_price equal to standard_price as a placeholder — Amazon flags it.

• Date format errors — Amazon needs ISO-8601 with timezone
• Lightning deals require pre-approval — submitting one without approval triggers 18540