Troubleshooting Call Completion
Identifying and resolving common issues with inbound and outbound calls
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Written by Dillin
Updated over a week ago

Troubleshooting Outbound Call Failures

Outbound calling, also known as “termination”, can be a tricky process to troubleshoot, but luckily, most termination issues are the result of a small handful of different causes. In this article, we will review the most common causes of call termination issues and illustrate what you can do to identify and resolve them.

Invalid caller ID

Perhaps the most common cause of call termination problems, particularly when setting up a new SIP connection, is caller ID. Caller ID is the service responsible for displaying your phone number to the device you are trying to call. When a call is rejected due to an invalid caller ID, you will receive the SIP response message “403 Caller Origination Number is Invalid D35”.

Why is my caller ID invalid?

Industry regulations mandate a strict policy regarding caller ID. For Telnyx to successfully terminate your call, we must pass a caller ID in +E.164 format. The +E.164 format is made up “+”, the caller’s country code, and the caller’s full phone number. Many times, PBXs and softphones do not automatically pass a caller ID. The caller ID will often either be blank or, if you are using a credential-based SIP connection, your SIP username. As a result, your call will automatically get rejected because there is no valid caller ID number.

How do I append a valid caller ID?

Unfortunately, this is where it varies. Each softphone and PBX has its own way of appending a caller ID to outbound calls. Fortunately, however, you can easily append a caller ID to any SIP connection using the Caller ID Override functionality within the Portal. To set a Caller ID Override, select the relevant SIP connection from the “SIP Connections” tab and select the “Outbound Options” icon to the right. From here, you can include a phone number that will be displayed on all outgoing calls made from this SIP connection.

Dialed number is not included in your whitelisted countries/regions

By default, all Outbound Voice Profiles are configured to allow traffic only to destinations in the United States and Canada. If you attempt to place a call to a number outside of this region, you will receive the SIP response “403 Dialed Number is not included in whitelisted countries D13”.

In order to resolve this, you must whitelist the region in the Outbound Voice Profile associated with the relevant SIP connection. You can do so by selecting “Outbound Voice Profiles” from the Mission Control Portal, selecting the relevant Outbound Voice Profile, and clicking the “+” button next to the relevant region. You can select individual regions, full continents, or add all regions and countries.

From here, you may be prompted to request level 2 verification, which authorizes you to make international calls. You can request this by hovering over your initials in the top right of the Portal, selecting “My Account”, and clicking the “Verifications” tab. Alternatively, you can find this page here. For more information on account verification, please see our Account Verification article.

403 - Forbidden

Slightly less common than the two issues above, a “403 Forbidden” can be returned to a caller for a variety of reasons. The most straight-forward cause of this SIP response is a failure to authenticate your SIP connection. If you are using the incorrect credentials on a credential-based connection or you are attempting to place a call from an IP address that has not yet been added to an IP-based connection, Telnyx will return a “403 Forbidden” and reject the call in order to protect your account from being charged for unauthorized use.

What if I am sure that I’m authenticated properly?

While an authentication issue is the most common cause of a “403 Forbidden”, it is not the only one. Other potential causes include:

  • Your Telnyx account is negative in balance.

  • The connection you are using to place the calls does not have an Outbound Voice Profile configured.

  • A token or tech prefix, if enabled on your FQDN/IP-based connection, does not match the token or tech prefix supplied in your SIP INVITE.

  • The caller origination number (caller ID) is a phone number that belongs to another Telnyx user.

503 - No routes found (or service unavailable)

While less common than a “403” error, a “503” error generally points to a routing issue for the specific destination. If you receive a 5xx response code, it’s advisable to contact support by starting a chat from the chat bubble on the lower right-hand corner of the Portal or by emailing, as this tends to require manual intervention. When contacting support, please provide a call example with the source and destination numbers as well as an approximate timestamp so that the relevant call can be located.

Further troubleshooting using the Debugging Tool

An exhaustive list of our SIP response codes can be found here. In general, a 403 error is the result of a discrepancy between what you are attempting to do and what your Telnyx account or PBX is configured to do. Other 4xx response codes, such as “404 Not Found” or “486 User Busy” generally indicate that there is an issue with the destination device. Alternatively, 5xx errors, while much less common, are often the result of a routing issue.

To gain additional insight when troubleshooting, you can leverage the debugging tool within the Portal to view the SIP logs and call flow for a specific call. For more information on using this tool, please see our Debugging article. The Debugging menu contains other features, such as the Web Dialer, which can be used to make calls directly from the Portal.

Troubleshooting Inbound Call Failures

Fortunately, inbound calls are susceptible to fewer problems than outbound calls; However, they can still be difficult to troubleshoot. If you are not receiving calls when you know you should be, this is generally an issue with either SIP registration or the authentication method selected when setting up your SIP connection.

SIP Registration (for credential-based connections)

Much like other SIP providers, Telnyx maintains a registrar of the devices associated with SIP connections. When you authenticate your SIP credentials on your softphone or PBX, a SIP REGISTER request is sent from your device to Telnyx, which tells Telnyx where to send the calls that are directed to your SIP URI.

If you are not receiving any inbound calls on a credential-based SIP connection, it is likely that we are not receiving the SIP REGISTER requests from your device. Please ensure that you have whitelisted traffic to and from the IP addresses and subnets listed in our What IPs do I need to whitelist? article.

IP and FQDN authentication

If you have configured your SIP connection to use IP- or FQDN-based authentication, then calls destined for your SIP URI will be sent to the user-provided IP address(es) along with the provided network ports. If there is a discrepancy in the IP address/port provided and the IP address/port your PBX is actively listening on, then the calls will not make it to your PBX.

Firewall and NAT configuration can also have an effect on inbound calls. Please ensure that you have whitelisted the traffic to and from the IP addresses and subnets listed in our What IPs do I need to whitelist? article. If you are using IP or FQDN authentication, it’s advisable that either your PBX is publicly exposed or that your router has the necessary port forwarding configuration enabled (for both the signaling (SIP) stream and the media (RTP) stream.

Further troubleshooting

If further troubleshooting is necessary, you can leverage the debugging tool within the Portal to view the SIP logs and call flow for a specific call, including those that were destined for your SIP URI but never reached your end device. For more information on using this tool, please see our Debugging article. You can also contact support by starting a chat from the chat bubble on the lower right-hand corner of the Portal or by emailing

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