Workflow is not starting automatically, needs manual execution - Messenger AI Chatbot

Hi there. I am new to n8n and just build my first workflow.
I have successfully automated Facebook Messenger to work with an AI. AI is replying as the representative for my Facebook page.
Everything working is fine only when I Manually press the button ‘Execute Workflow’, it receives the message and reply is given to the user.
I saved the workflow and toggled the Active button to ‘on’.
I would like to run this workflow whenever there is a message from user. But it’s not happening I need to manually start the workflow. I am on 14 day trial and using n8n cloud to try it out.
Thank you in advance for your kind attention and help.

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