I'm pretty sure there must be an API. Businesses want to respond with a text immediately and provide a way for people to interact with the company even outside

I'm pretty sure there must be an API. Businesses want to respond with a text immediately and provide a way for people to interact with the company even outside business hours. What would be cool is a way for the app to hand over control to a manual WhatsApp user (i.e. the employee) if necessary and continue the conversation there.