To add a free chat bot to your Facebook account, follow these steps:

Go to the Facebook Developer website (https://developers.facebook.com/) and log in using your Facebook account.

Click on the “Create” button in the top right corner.

From the dropdown menu, select “Create a New App.”

Fill out the necessary information and click “Create App.”

On the dashboard, click on the “Add Product” button and select “Messenger.”

Click on “Set Up” under the Messenger section.

Follow the prompts to set up your chatbot, including setting up a webhook and configuring the chatbot’s behavior.

Once your chatbot is set up, click on the “Generate Token” button to get your chatbot’s access token.

Go back to your Facebook page and click on the “Add a Button” button in the top right corner.

Select “Contact Us” from the dropdown menu and click “Next.”

From the options available, select “Send Message” and click “Next.”

In the “Send Message” section, enter the access token you generated in step 8 and click “Save.”

Your chatbot is now added to your Facebook page and can be accessed by visitors through the “Send Message” button.