You can set the opening message after accessing the botcake admin page: Select Automation -> Welcome Message:
With the opening message, new subscribers will better understand the purpose of your Messenger bot in the meantime.
Only customers who have never chat with your Fanpage ever since installing chatbot will see the "Start" button -> if they press the "Start" button, they will receive the content you wrote in the "Welcome Message".
How to check:
You can check the message content in the user role by visiting the Fanpage and using your personal Facebook account to chat (delete the conversation of that account with Fanpage will see the "Start" button)
Useful information that you should include in your Welcome Message:
Introduce your page.
What promotions do you have?
And anything that you think is important (like opening hours, hot trends, or even your favorite animation, etc.).
Remember, anyone who clicks the "Start" button, they will receive Welcome Message from your page.
Note: You can turn off the "start" button in Messenger in Settings -> Generals.