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HTTP_STATUS_PRECOND_FAILED
It is commonly returned for conditional headers such as If-Match, If-None-Match, If-Unmodified-Since, or WebDAV conditional requests. The resource may have changed since the client last read it.
Fetch the current representation and validators before retrying. Do not discard concurrent changes by sending an unconditional overwrite unless that behavior is intentional.
The relevant condition might come from If-Match, If-Unmodified-Since, or another conditional header. Compare the validator or date sent by the client with the current selected representation. A failed precondition is useful concurrency information; removing the condition blindly can convert a safe update into an unintended overwrite.
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