What's the best approach to programming the end of the call to make sure its smooth? I cant find the end Call Phrases in dashboard, can it be used using the api? And if so, is it reliable (or is it deprecated)? I have used the end call function with gpt-4o. It ends the call very suddenly and looks unnatural. I cant find options to fix that so I turned it off.

It can be used reliably. Here is an example request payload for endCallPhrases

curl -X PATCH \
  https://api.vapi.ai/assistant/YOUR_ASSISTANT_ID \
  -H "Authorization: Bearer YOUR_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "endCallPhrases": [
      "goodbye",
      "bye",
      "talk to you later",
      "have a great day",
      "see you soon"
    ]
  }'

I did quite a bit of testing on this, I found using a combination of endCall and endCallPrases, combined with prompt, worked well. I wrote an article on this. https://patrickmichael.co.za/how-do-you-end-calls-smoothly-vapi-complete-guide-professional-voice-agent-call-endings