Calling an active process using API

Can you explain the use case a little more?

There are a couple of options here:

1. in your active process instance you could implement a time-based "wait/check/wait" loop that fetches a flag from the database that your chat bot process writes to. If the flag indicates no action received then you wait, else you flow to the approval step.
2. in your active process instance you can implement a "listener" that is waiting for a process-to-process or external-to-process message  - https://docs.appian.com/suite/help/22.2/Receive_Message_Event.html - and use that to control the flow of your active process

In either option consider how you'll handle the scenario when a message never arrives - don't assume that one will and make provision to handle this.