Note: The error code is the last 3 digits of the code you see in the error notification. For example, if you see the error notification Call failed (code: 2202404), the error code is 404.
If you are receiving Zoom Phone error 503: Your service is affected by a network issue. Please check your network and try again later., this means that a routing error might be preventing your call from getting through.
Contact your Zoom Phone admin for help. You may need to change your network firewall or proxy server settings.