Overview

When sellers see error code 100521 on a product page, Amazon is placing the listing in a manual‑review queue. The hold can last as long as 48 hours and is automatically applied when a brand‑new item is submitted or when a live listing receives substantial changes. Knowing why the hold occurs helps sellers stay calm and avoid creating duplicate entries while Amazon evaluates the content.

Key Points

• Error 100521 signals a review, not a denial — The code tells you Amazon is examining the listing; it does not mean the offer has been rejected.
• Maximum review period is 48 hours — Amazon advises sellers to allow a full two‑day window before taking any further steps.
• Do not open a second listing for the same product — Adding a duplicate ASIN while the original is under review can trigger policy violations and further delays.
• Notification arrives only if action is required — If Amazon needs more data, a message will appear in Seller Central; otherwise the listing goes live automatically after the review.
• High‑scrutiny categories are more prone to holds — Items in gated or restricted groups, such as health supplements or electronics, often trigger the review flag.

How the Manual Review Process Works

1. Submission triggers automated screening — When you upload a new product or edit a major attribute (e.g., title, images, bullet points), Amazon’s algorithms scan the content.

   • Example: A seller adds a new “organic turmeric capsule” to the health‑supplements category; the system flags the claim “organic” for closer look.

2. System assigns review code 100521 — If the automated check finds potential compliance issues, it tags the listing with error 100521 and moves it to a human‑review queue.

   • Example: An existing kitchen‑tool listing receives a revised title that includes the phrase “best‑selling”; the change prompts a manual check.