---
title: SANBDOX_NOT_LISTENING
product: vercel
url: /docs/errors/SANDBOX_NOT_LISTENING
type: reference
prerequisites:
  []
related:
  - /docs/vercel-sandbox
summary: The Sandbox is not listening on the requested port. This is an application error.
install_vercel_plugin: npx plugins add vercel/vercel-plugin
---

# SANBDOX_NOT_LISTENING

The `SANDBOX_NOT_LISTENING` error occurs when you are trying to access a Sandbox that is not listening on the requested port. This could happen if the port is malconfigured, or the process running on that port has exited.

**Error Code:** `502`

**Name:** Bad Gateway

## Troubleshoot

To troubleshoot this error, follow these steps:

1. **Verify the configured port:** Make sure that the `ports` field used in `Sandbox.create` matches the port your application is listening on. Follow the [documentation](/docs/vercel-sandbox) to learn more
2. **Check the Sandbox history:** Navigate to the [Sandboxes dashboard](/d?to=%2F%5Bteam%5D%2F%5Bproject%5D%2Fobservability%2Fsandboxes\&title=Go+to+Sandboxes), select the one you are accessing, and check the history section to see which commands were run and if any errors occurred


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