CRITICAL BUG - SIP re-INVITE rejected (486)

Support Help
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Impact: All call queue/hunt group transfers fail

Description: When NetSapiens sends a mid-call re-INVITE to update the media path (standard SIP behavior when an agent answers), Retell AI responds with 486 Rejected instead of accepting the SDP update. This makes Retell AI incompatible with ANY call queue system that uses re-INVITE for media path updates.

RFC 3261 Section 14: re-INVITE is standard for session modification.

Rejecting it breaks call queues, consultative transfers, and hold/resume.

Workaround attempts: - Tried blind transfer via Forward Always (still triggers re-INVITE) -

Tried auto-attendant relay (still triggers re-INVITE) -

NetSapiens doesn’t send REFER to external parties on internal forwards Request: Fix re-INVITE handling to accept SDP updates per RFC 3261.

SIP Trace/Log file provided upon request (mark@amplex.net)

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Based on the available documentation, there is a known issue with SIP session refresh handling that may be related to your re-INVITE problem(1). A user reported that their carrier enforces a 300-second Session-Expires timer on inbound calls requiring a refresh at 150 seconds, and their inbound calls were dropping at exactly 150 seconds because Retell was failing to send the required re-INVITE/UPDATE when acting as the refresher=uac(1).

The user specifically asked: “Is there an opportunity to enable these sip options?”(1) This suggests that Retell AI’s SIP server may not currently handle mid-call re-INVITE/UPDATE messages as expected per RFC 3261.

For your NetSapiens call queue scenario, Retell AI does support SIP integration through Elastic SIP Trunking, which connects your telephony provider’s SIP trunk directly to Retell(2). Retell’s SIP server supports TCP, UDP, and TLS transport methods(2).

However, I don’t have explicit documentation confirming that Retell AI properly handles mid-call re-INVITE messages for SDP updates during call queue operations. The available sources discuss call transfer capabilities using SIP REFER for cold transfers(2), but don’t detail re-INVITE handling for media path updates.

Immediate steps you can take:

  1. Contact Retell AI support directly with your SIP trace/log file at the email you provided
  2. Check out these support channels:

Since this appears to be a technical SIP protocol compliance issue that’s not addressed in the current documentation, Retell AI’s engineering team would need to investigate your specific SIP traces to determine if their server can be updated to accept re-INVITE messages per RFC 3261 Section 14.

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How do I contact support directly? Please provide contact information.

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Based on the available sources, here are the official Retell AI support channels:

Discord Community
Join the Retell AI Discord server at https://discord.com/invite/wxtjkjj2zp for community support and direct interaction with the Retell AI team(1).

Documentation
Visit the official documentation at https://docs.retellai.com/general/introduction for technical guides and references(1).

Certified Partners
For professional implementation assistance, you can hire a certified Retell partner at https://www.retellai.com/partners(1).

Sales Contact
To book a demo or speak with the sales team, visit https://retellai.octolane.com/(2).

I don’t have a direct email address or phone number for Retell AI technical support in the available documentation. Your best path for urgent technical issues like the SIP re-INVITE problem would be to post in the Discord community where Retell AI team members are active, or reach out through the sales contact link to request escalation to engineering.

5

Hello @mark

We don’t support we don’t support re-INVITEs yet.