How to Limit Responses and Customize Agents Beta Integration?

Hello,

I am planning to use Agents Beta, but I couldn't find a solution that allows me to limit and control the agent to respond to just one question and then require payment through my system before continuing. I also couldn’t locate such a function in the API documentation. Is there a list of available functions somewhere?

Additionally, I have a few more questions:

Is it possible to connect the agent with another AI model? Currently, there is a command input field integrated with the D-ID model, and it displays the placeholder text "type here." Can this text be customized to something else?

If integrating Agents Beta with another AI model is possible, how would its usage be billed?

Thank you in advance for your help!