The request should be conditional (for example with If-Match) to avoid lost updates.
Quick facts
When does it occur
The request should be conditional (for example with If-Match) to avoid lost updates.
It belongs to the 4xx Client Error class of responses, defined in RFC6585#3.
Browse all codes in this class: 4xx Client Error
How to fix it
Add If-Match or If-Unmodified-Since with a current ETag to the request.
Common causes
How to fix it
Double-check the URL, return to the homepage and search again, or retry later.
Add If-Match or If-Unmodified-Since with a current ETag to the request.
Review access logs and permission rules for the affected path, and confirm routing and security policies.
Frequently asked questions
428 belongs to the 4xx Client Error class and is generally not cached for long; behavior is controlled by Cache-Control.
4xx Client Error: The request should be conditional (for example with If-Match) to avoid lost updates.
Sources & standards
Updated 2026-08-18
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