Agent failed to transfer the call to Unknown number | ElevenLabs | Page 1

mighty sealBOT Apr 13, 2026, 7:50 PM

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AI-generated Answer for cauliflower9481

Likely cause and how to fix

Destination not configured: transfer_to_number only works if the destination exactly matches a preconfigured transfer rule. Add the phone number/SIP URI under Agent > Tools > System tools > Transfer to Human, and have the LLM pass a transfer_number that matches one of those rules. Use E.164 for phone numbers or a valid SIP URI. (elevenlabs.io)
Unsupported integration path: if the call was connected via the Twilio “register call” endpoint, transfers are not available. Use an imported Twilio number (native integration) or SIP trunking instead. (elevenlabs.io)
Transfer type prerequisites not met:
- Blind transfer is only supported with imported Twilio numbers and must be set via the JSON editor.
- SIP REFER requires the call to be over SIP and your trunk to allow REFER; no warm-transfer message is supported.
  Verify your rule’s transfer_type against your telephony setup. (elevenlabs.io)
Remote command used without tool enabled: if you triggered a transfer via real-time monitoring, the transfer_to_number tool must already be configured on the agent. (elevenlabs.io)

Where to confirm the exact failure

Open Call History; failed calls show a red reason string (e.g., formatting/permission/routing issues). Use that message to pinpoint configuration gaps. (help.elevenlabs.io)

Quick checklist

Add a Transfer to Human rule with the exact destination (E.164 or SIP URI) and a matching condition. (elevenlabs.io)
If using Twilio, import the number into ElevenLabs rather than using the register-call flow. (elevenlabs.io)
Test with Conference transfer first; add Blind or SIP REFER only if your setup supports them. (elevenlabs.io)

If you share the Call History error text, I can point to the precise doc-backed fix. (help.elevenlabs.io)

wanton ferry Apr 13, 2026, 7:58 PM

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i use Conference transfer and get unknown number

mighty sealBOT Apr 13, 2026, 7:58 PM

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AI-generated Answer for cauliflower9481

Short answer

Conference transfer is the default, but only Blind transfer preserves the original caller ID. If the callee is seeing “Unknown number” and you want them to see the caller’s CLI, switch the rule’s transfer_type to blind (requires the native Twilio integration and JSON editor). (elevenlabs.io)

What to check/fix

Use the native Twilio integration. Blind transfers and warm transfer messages are only supported when your agent’s phone number is imported via the native Twilio integration. (elevenlabs.io)
Set transfer_type to blind in the transfer_to_number tool rule (Edit as JSON), and ensure the destination is in E.164 format and preconfigured in your rule set. The tool call must pass a transfer_number that matches a configured rule. (elevenlabs.io)
If you’re using the “register call” Twilio pattern instead of the native integration, call transfers aren’t supported. Use the native integration if you need transfers. (elevenlabs.io)
For SIP REFER transfers, warm transfer messages aren’t supported; ElevenLabs automatically includes X-Caller-ID and X-Conversation-ID headers if you rely on SIP-side caller identity handling. (elevenlabs.io)
If a transfer attempt is failing (not just showing “Unknown”), check Call History for the exact error reason (for example, “Missing dynamic variable after agent transfer”). (help.elevenlabs.io)

If you share your current transfer_to_number rule JSON and whether you’re on the native Twilio integration, I can point out the exact field to change. (elevenlabs.io)

Sources:
Transfer to number | ElevenLabs Documentation
Transfer to number | ElevenLabs Documentation
Transfer to number | ElevenLabs Documentation
Register Twilio calls | ElevenLabs Documentation
Transfer to number | ElevenLabs Documentation
Where can I locate the reason for my call failing? – ElevenLabs
Transfer to number | ElevenLabs Documentation

wanton ferry Apr 13, 2026, 7:59 PM

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i dont use twilio

mighty sealBOT Apr 13, 2026, 7:59 PM

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AI-generated Answer for cauliflower9481

Got it—using ElevenAgents without Twilio is supported.

Key facts from the docs:

Call transfer works with either Twilio numbers or SIP trunking. You can transfer to standard phone numbers (E.164) or SIP URIs via the transfer_to_number tool. (elevenlabs.io)
Conference transfer is the default and works with SIP. Warm transfer messages (agent_message) are only available with the native Twilio integration. (elevenlabs.io)
Preserving the original caller ID is only documented for blind transfers, and blind transfer is available only with the native Twilio integration. The docs do not state caller ID preservation for SIP or for conference transfers—so “Unknown number” at the destination can occur outside of Twilio. (elevenlabs.io)
If you’re on SIP and need a direct handoff, you can use SIP REFER transfer (your SIP trunk must allow REFER). You can attach custom SIP headers; ElevenLabs also auto-includes X-Conversation-ID and X-Caller-ID. Note: headers apply only to SIP REFER, not to conference transfers. (elevenlabs.io)
Make sure your SIP trunk number is properly imported and matches the exact format you dial (leading + consistency); mismatches will break routing. (elevenlabs.io)

If you share whether you’re transferring to a phone number or SIP URI, and whether SIP REFER is enabled on your trunk, I can point you to the exact configuration snippet in the transfer_to_number tool. (elevenlabs.io)

wanton ferry Apr 13, 2026, 8:05 PM

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i use phone number

#Agent failed to transfer the call to Unknown number