# upstream connection failed: The upstream host could be down

The end-user receives this message on sign-in:

```
Message: upstream connection failed
Action: The upstream host could be down
```

This indicates the Agilicus Connector is up, and the user was able to sign in correctly, however, the customer-supplied application is either down, or unreachable from the Agilicus Connector.

![Upstream Connection Failed: Troubleshooting guide showing potential causes, including a down upstream host, with a diagram illustrating the network path and potential failure points.](https://www.agilicus.com/www/7e287088-diag-1024x344.jpg)    A common issue is a change in IP/port of the application, you may change this as below.

![Upstream Connection Failed: Troubleshooting network connectivity issues. Diagram illustrates potential network problems causing upstream host to be down, affecting service availability. Learn to diagnose and resolve upstream connection failures.](https://www.agilicus.com/www/7d4863b1-network-1024x461.png)    To diagnose the issue, use the detailed stats from the connector overview page:

![Agilicus upstream connection failed: Diagram illustrating a failed connection between a client, Agilicus, and the upstream host, indicating a potential issue with the upstream host being down or unreachable.](https://www.agilicus.com/www/fd868928-image-1024x456.png)