Integrate chatbots into messenger

Question

I am integrating an existing chatbot to automatically reply to messenger. When it comes to the requests post graph step:

response = requests.post(
                "https://graph.facebook.com/v11.0/me/messages?access_token="
                f'{getenv("FB_PAGE_ACCESS_TOKEN")}',
                json=request_body,
            ).json()

So is there any cost or limitation when calling this API, and if you want to expand it, is it complicated? Thank you!