# 54003: Invalid If-Match header

Log Level: ERROR

## Description

The specified If-Match header cannot be used for concurrency control.

### Possible causes

* The value specified in the If-Match header is not a valid Sync object revision.

### Possible solutions

The value you provide should be a revision assigned by the Sync service when interacting with an object.

* In SDKs, this is the `revision` field, part of the object descriptor.
* When using REST (e.g. via the Twilio Helper libraries) this is the `ETag` header provided in responses.