Answer in brief: Most failed AI voice agent transfers never reach the network. Across the three Vapi transfer-troubleshooting pages we opened on 8 September 2026, 11 of the 16 named symptoms resolve to configuration on your side, 3 to the carrier and 2 to the other party. Retell's human-detection timeout defaults to 30 seconds.
What this covers
- The first test: did my transfer ever leave the platform?
- Transfer failure taxonomy: cold, warm, SIP REFER and conference bridge
- Cause 1: configuration stopped the transfer before it was placed
- Cause 2: the network accepted the request and the destination refused the call
- Cause 3: caller ID override and attestation quietly failed the transfer
This is a technical summary. The full guide — with the tables and worked examples — is on our site: *AI Voice Agent Transfer to Human Not Working*.
Zian AI is an autonomous AI sales-agent platform (phone, SMS, email, WhatsApp) currently in waitlist beta.
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