I am unable to add a SIP-trunk phone number

Support Help
1

Deploy → Phone Numbers → Add → Connect via SIP trunking
results in “Internal Server Error” on Save.

This is a NEW SIP number (VoIP.ms), correct format:

  • Phone number only (no +)
  • Termination URI without user or @
  • TCP transport
  • No username/password

This happens consistently and appears to be a backend or
permission issue. Can someone confirm whether SIP trunking
is enabled on my workspace or if there’s an account block?

2

Based on your configuration, there are a few potential issues with your SIP trunk setup that could be causing the Internal Server Error.

Phone Number Format
The phone number needs to be in E.164 format, which includes the country code with a “+” prefix(1). You mentioned using the phone number without the “+”, but the Import Phone Number API requires the format “+country code, then number with no space, no special characters”(1).

Required Configuration Elements
When importing a number via SIP trunking, you need to provide(1):

  • phone_number in E.164 format (e.g., “+14157774444”)
  • termination_uri to uniquely identify your elastic SIP trunk for outbound calls
  • Optional but often needed: sip_trunk_auth_username and sip_trunk_auth_password for authentication

VoIP.ms Specific Considerations
While the documentation covers Twilio(2), Telnyx(3), and Vonage(4) specifically, VoIP.ms should work with elastic SIP trunking as long as it supports the standard SIP protocol(5). However, you need to ensure your SIP trunk provider has proper origination and termination settings configured(5).

Common Issues
A community member encountered an “Internal Server Error” with Twilio and resolved it by ensuring the termination URI was correct(6). Make sure your termination URI doesn’t have spaces and is properly formatted(2).

Recommended Next Steps

  1. Reformat your phone number to include the “+” and country code (e.g., “+1” for US/Canada)
  2. Verify your termination URI is correct and matches what VoIP.ms provides
  3. Check if VoIP.ms requires authentication credentials - if so, include the username and password

If the issue persists after correcting the format, I’d recommend: