Any story or media block you create will be triggered as soon as a user clicks on your Send to Messenger button.
Here’s how to do it:
Go to your facebook connected Botsify chatbot and select Growth Tools. When the sidebar expands click on Send to Messenger.

Select a story if you want to initiate a story once a user clicks on your send to messenger button or choose a media block.

Click on Generate Code and you will see the following display options of your send to messenger button:

Choose the look you want for your send to messenger button and copy and paste this code on your website.
You can follow the same steps to send a media block through your send to messenger button.