428 Precondition Required

HTTP 428 Precondition Required tells the client that the server requires the request to use conditional headers (like If-Match) to prevent the lost-update problem in concurrent edits.

APIs enforcing optimistic concurrency control to prevent silent overwrites.

• PUT/PATCH without If-Match header
• Server enforces ETag-based versioning
• API designed to prevent race conditions

• Include If-Match header with current ETag in PUT/PATCH requests
• Fetch the resource first to get the current ETag
• Implement optimistic locking client-side

HTTP/1.1 428 Precondition Required
Content-Type: application/json

{"error":"If-Match header required"}