# Reject handling

Unexpected messages are rejected by Revolut FIX Gateway by sending the [**`3` (Session Level Reject)**](/docs/guides/exchange-fix-api/introduction-to-the-exchange-fix-api/system-overview#session-level-messages) message. 

Possible rejection reasons are: 
- Missing mandatory tag
- Incorrect tag value or no tag value
- Unknown message type
- Tag provided multiple times 
- Other errors