Troubleshoot the Dialer

Article author
Dustin Nathaniel Keys


If you're experiencing issues with the dialer like audio cutting out, call connection errors, or trouble hearing the person on the call, a few troubleshooting steps can help.

Where Are My Calls?

Looking to access previous calls? Check out Access, Manage, and Share Call Recordings.

Review the following sections to troubleshoot the dialer.

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Number Marked as Spam

You must take steps to protect your caller reputation. Check out Cold Calling Best Practices for advice, laws, and regulations you should follow to ensure your phone number isn't screened or marked as spam.

If your phone number has been screened or marked as spam, you can get a new Apollo phone number.

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Call Connection Error

If you encounter a call connection error like Call Connection Error - The call cannot be completed as dialed due to an unknown error, it usually indicates a caching problem with your internet browser.

To resolve this issue, clear your browser's cache:

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Audio Cuts Out

If audio drops intermittently causing dead air, you may be experiencing an unstable network connection. The dialer requires a high-speed, low-latency network connection.

First, perform a speed test to verify your network connection speed.

If your connection is slow, follow these steps to improve your odds of a good dialer connection:

  • When possible, use an ethernet cable rather than a WiFi connection. Wired connections are more reliable.
  • Close extra tabs in your internet browser. Tabs take up bandwidth.
  • Exit any other programs that use bandwidth.

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Unclear Audio

If you maintain a steady connection when using the dialer, but you experience a garbled or otherwise unclear audio connection, follow these steps:

  • Use a wired headset instead of your built-in computer microphone. A wired connection will deliver a more reliable audio experience.
  • Reduce ambient noise, such as nearby speakers or fans.
  • To avoid audio clipping, make sure your microphone isn't too close to your mouth.
  • Adjust the microphone levels in your computer settings. Your input may be too loud.
  • Ensure that your computer has sufficient memory to process the dialer. Apollo recommends that your computer have at least 16GB of RAM.
  • Close any applications that you don't need during calls.
  • Antivirus software can be resource-heavy. Deactivate your antivirus program while you make a call.
Stay Safe

Only deactivate your antivirus software as a last resort to troubleshoot an issue. Keep your network and computer safe at all times.

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No Audio

The dialer requires 16GB of RAM, and we recommend wired headphones for calls. Confirm that both your hardware and software meet these requirements. If there's still no audio when using the dialer, try the following steps:

  • If you use an external headset, confirm you have attached your headset correctly.
  • If you use a wired headset, plug your headset into a different port. Ports can fail without any warning.
  • Confirm you have selected the right device in your sound settings. For example, your computer's audio output might be set to your computer speakers, even when your external headset is connected to the computer.
  • Try connecting a different external headset.
  • The Apollo dialer integrates with Twilio. Run this Twilio-provided test to help pinpoint your issue.
  • Try a different internet browser. If you use Chrome, try the dialer with Microsoft Edge or Firefox.
  • Confirm you have given your internet browser permission to play sound:
    • If you use Chrome, go to chrome://settings/content/sound to ensure you have enabled the Sites can play sound button.
    • If you customize which sites can play sound from your browser, verify that is listed in Allowed to play sound.
  • Confirm you have given your internet browser permission to use your microphone:
    • If you use Chrome, go to chrome://settings/content/microphone to ensure you have enabled the Sites can ask to your mic button.
    • If you customize which sites can use the mic, verify that is listed in Allowed to use your microphone.

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No Ring Tone; One-way Audio

If you don't hear a ringtone when using the dialer to make a call, or only one side of the call can hear audio, you may experiencing high post-dial delay (PDD). This means Twilio sent a connection request to the telecom operator, but it’s taking a long time to respond.

PDD is most likely caused by the caller and receiver being geographically far away from each other. This means it takes time to establish a connection between the two parties. Using a VPN can add to the delay when establishing the connection.

If you use a VPN, there are 2 options:

  • Disconnect from your VPN when making calls.
  • If you can't disconnect from your VPN, coordinate with your engineering or IT team to allow Apollo permanent access via firewall and VPN rules.

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Ring Tone, but No Audio

If you hear a ring tone but no audio after the call is answered, the issue is most likely due to the telecom operator. Try to make the call again later.

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General Errors

Apollo recommends you use a computer with at least 16GB of RAM and that you use a USB-based headset when making calls. The latency in a wireless headset can cause delays.

If your hardware meets the specifications, troubleshoot your browser and computer.

Troubleshoot Your Browser

Your internet browser can consume too much RAM or have other issues that result in poor connection quality. Troubleshoot your browser to resolve these issues.

Troubleshoot Your Computer

If issues with the dialer aren't related to your browser, review your network settings to ensure that your compupter is allowing the needed network connections.

The following 2 network settings are most likely to interfere with the dialer:

  • A Windows firewall
  • A VPN


If you use a Windows firewall, it can interfere with the dialer. You can either deactivate the firewall entirely or allowlist Twilio's full IP and port ranges.

To deactivate the Windows firewall:

  1. Open Control Panel and click System and Security.
  2. Click Windows Defender Firewall.
  3. Click Turn Windows Defender Firewall on or off.
  4. Click Turn off Windows Defender Firewall for both private and public network settings.

With the Windows firewall deactivated, try the dialer again.

If you can't deactivate the Windows firewall, check your firewall configuration. The firewall needs to give outgoing User Datagram Protocol (UDP) access to the public internet from the internet browsers that use the dialer. The firewall also needs to allow return traffic in response.

If you're on a restricted network, you must allowlist Twilio's full IP and port ranges. Once you update your network infrastructure, enable your account's production traffic to use the IP ranges. For more information about Windows firewall, check out Microsoft learning center.


VPNs might affect which edge server Twilio uses to route traffic. This can add some latency to calls. For example, if you're in the US trying to make a call to the US without a VPN, Twilio uses an edge location in the US to route the call. However, if you use a VPN that connects you to a server in Australia for the same call, Twilio might route the call differently and negatively impact the call quality.

If you use a VPN, there are 2 options:

  • Apollo recommends you disconnect from your VPN when making calls.
  • If you can't disconnect from your VPN, coordinate with your engineering or IT team to allow Apollo permanent access via firewall and VPN rules.

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Enable Call Debugging

If the troubleshooting guidance in this article doesn't fix your issue, enable call debugging in Apollo and then contact Apollo support.

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