---
page_type: error
code: 54003
message: "54003: Invalid If-Match header"
level: ERROR
product: Sync
---

## Error - 54003

### Sync: Invalid If-Match header

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.