# Challenge Process
The Challenge Process begins when **Validating Nodes (VNs)** detect a discrepancy in the transaction processing.
Challenge Process
**These discrepancies can arise from various issues, such as:**
* A mismatch between **off-chain orders** processed by the sequencer and their corresponding **on-chain orders**.
* Off-chain orders being processed **out of sequence** by the sequencer (e.g., an order that should have been processed first was handled later).
* **Exclusion** of an order from the blockchain entirely by the sequencer, even though it was a valid order that was processed **on-chain**.
{% hint style="info" %}
When VNs detect one of these problems, they can trigger a **challenge**.
{% endhint %}
