The SIP 500 error with telephony_provider_unavailable indicates the telephony provider encountered an internal server error(1). This disconnection reason means the telephony provider is unavailable or experiencing errors(1).
Troubleshooting steps:
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Verify your SIP trunk configuration - Double-check your configuration and ensure you imported the correct information(2). If the configuration is incorrect, delete the imported number and re-import it(2).
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Check your SIP endpoint format - Ensure your SIP endpoint uses the correct format with
;transport=(semicolon) rather than.transport(3). The endpoint should follow the pattern likesip:sip.retellai.com;transport=tcp(3). -
Review detailed call logs - The call detailed log contains the disconnection reason, SIP error code, and error message to help identify the root cause(2).
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Contact your telephony provider - Since the SIP 500 error indicates a server-side issue with your telephony provider, open a ticket with Telnyx to investigate the error on their end(2). Even though their logs show everything went through, the 500 status code suggests their server had trouble processing the transfer request(2).
The error specifically points to a telephony provider availability issue rather than a Retell platform issue(2).