Overview

Error 90121 is a feed processing error that Amazon sellers encounter when data submitted through product listings or inventory feeds doesn't match the required formatting pattern. This validation error can block listing updates and new product submissions, making it essential for sellers to understand the root causes and how to resolve them quickly.

Key Points / What Sellers Need to Know

• Pattern mismatch is the root cause — Error 90121 triggers when a value in your feed doesn't conform to the specific format or pattern Amazon expects for that field, such as SKUs, model numbers, or other standardized identifiers.
• Special characters are a common culprit — Unauthorized characters, extra spaces, or incorrect symbols in your data fields will cause this validation to fail.
• The feed processing report is your best diagnostic tool — Amazon's feed processing summary report will tell you exactly which field and which pattern requirement triggered the error, so always check it first.
• Resubmission is required after corrections — Once you've identified and fixed the formatting issues, you'll need to resubmit your feed for the changes to take effect.

Common Causes of Error 90121

This error typically surfaces when sellers are uploading product data through flat files, inventory feeds, or API submissions. The most frequent triggers include using incorrect separators between values, mixing up character cases when the field requires a specific format, and including spaces or special characters that fall outside the allowed set. For example, a SKU field might require only alphanumeric characters and hyphens, but if you accidentally include an underscore or a period, the pattern validation will reject the entire entry. Similarly, model numbers and product identifiers like UPCs or EANs have strict formatting requirements that must be followed precisely.

How to Diagnose the Issue

The first step in resolving Error 90121 is to download and review your feed processing summary report from Seller Central. This report will identify the specific pattern requirement that your data failed to match, often expressed as a regular expression or format description. Look for the field name and the expected pattern, then compare it against the values you submitted. Pay close attention to details that are easy to overlook, such as leading or trailing spaces, incorrect use of uppercase versus lowercase letters, and the wrong type of dash or separator character. If you're working with bulk uploads, filtering your spreadsheet to isolate the problematic rows can save significant time.