I'm integrating vapi.ai in my crm and need to integrate a number of their APIs, in php I don't need the complete integration with my crm but only the bare integration code in php (compatible with php 7.4+) those are the integrations i need: how to push an assistant (with which llm to use, transcription, tts, prompt, etc) how to view the list of calls made by a certain assistant how to view the cost of a certain call how to see my total current credit