Overview

Amazon sellers who submit refunds or adjustments via XML or tab‑delimited feeds sometimes encounter error code 18018. The error appears when any refund field contains a negative number, which Amazon’s feed engine rejects. Resolving the issue is critical for sellers who rely on bulk or automated refund processing to keep buyer experience smooth.

Key Points

• Refund amounts must be entered as positive values — Amazon treats every figure in a refund feed as a credit to the buyer, so the system expects a non‑negative number such as 5.99 rather than ‑5.99.
• Negative entries trigger an automatic rejection — The moment the parser finds a minus sign in a refund column, it stops processing that line and returns error 18018.
• Feeds cannot be used to charge buyers — Supplying a negative amount would imply a debit to the customer’s card, a transaction Amazon does not allow through its adjustment feed interface.
• Additional charges must be buyer‑initiated — If a seller needs to collect extra fees after an order ships, the buyer must contact Amazon directly to request a recharge; the seller cannot initiate it via a feed.
• Automated systems need absolute‑value logic — Scripts, third‑party integrations, or spreadsheet templates that output negative numbers will repeatedly generate the error until they are updated to output the absolute value of each refund component.

How Error 18018 Happens

1. Feed preparation — A seller builds a refund file, for example a tab‑delimited row that includes RefundAmount = -12.34. The negative sign is often used in accounting to denote a credit, but the feed format expects a positive number.
2. Amazon’s parsing engine reads the file — During ingestion, the system scans each column. When it encounters -12.34 in the refund field, the validator flags the value as invalid because it violates the “positive‑only” rule.
3. Processing stops and error code is returned — The engine aborts the current record, logs error 18018, and sends the failure response back to the seller’s upload report, indicating that the line was rejected due to a negative refund amount.