I want to use warm-transfer-experimental as the transfer plan however we also want the destination to press a key before making the transfer. Which seems like that can only be done using the warm-transfer-twiml

You're correct: if you want the destination to press a key before the transfer completes, you need to use the warm-transfer-with-twiml mode. Here’s a sample configuration using TwiML to prompt for a key press:

json
"transferPlan": {
  "mode": "warm-transfer-with-twiml",
  "twiml": "<Say>Please press 1 to accept the call.</Say><Gather numDigits=\"1\" timeout=\"5\"/><Say>No input received. Goodbye.</Say>"
}

This approach is not supported in warm-transfer-experimental mode. See the [Vapi documentation](https://docs.vapi.ai/call-forwarding#5-warm-transfer-with-twiml) for more details. Source: - [Vapi Call Forwarding Documentation Warm Transfer with TwiML](https://docs.vapi.ai/call-forwarding#5-warm-transfer-with-twiml)

Does this transfer mode work for you?