So it's all about dialogflow bot integration with facebook messenger.
I understood your requirement, and i can do this , the connection of your existing bot or to be developed bot with facebook messenger with verification process.
Till now i had developed many chatbots for facebook messenger using webhooks and API integrations.
I can show you demo of my restaurant bots , gas agency bot and much more during chat.
Let's have a talk , it will be great working.
Thanks