# Identify a firewall or proxy server problem

Source: https://developer.avalara.com/products/ecm/integration-guides/document-management/fys7292932125587/

Guide: Exemption Certificate Management (ECM)

# Identify a firewall or proxy server problem

Learn how to identify and resolve connection issues caused by firewalls or proxy serversblocking AvaTax URLs.

## What you might see or experience

If your software is unable to contact AvaTax, most API calls you make will produce anerror. So, let’s begin by explaining how we can identify whether a connectionproblem exists.

-   Most API calls return an error.
-   You can't connect to AvaTax from your software.
-   The AvaTax API server page doesn't load on your computer.

## Why this happened

Your network connection to AvaTax isn’t working. This can happen if a firewall orproxy server is blocking access to AvaTax URLs.

## What might help

Steps

1.  Visit the AvaTax API server from your desktop computer or mobile phone.Try both of these URLs:
    -   **Sandbox environment:**[https://sandbox-rest.avatax.com](https://sandbox-rest.avatax.com)

    -   **Production environment:**[https://rest.avatax.com](https://rest.avatax.com)

2.  If your connection is working, you’ll see a page withlinks to AvaTax resources.

    ![rest-avatax-com](https://knowledge-be.avalara.com/bundle/hxd9079947903116_hxd9079947903116/page/pwh3723490734402.image?_LANG=enus)

3.  If you can’t see this page on your desktop computer at work, but youcan see this page from a mobile phone on the public internet, you likelyhave a networking issue. There’s a chance that your office has afirewall or proxy server that enforces some limits on your networkconnectivity. Contact your corporate IT department for moreinformation.