How Do I Transition from Facebook Lead Ads Default Chat Template to ManyChat Automation?

I am running Facebook Objective > Lead Ads.
When you run this way,   you cannot select manychat integration.  
So what I am trying to do is, use the default chat, which is working great so far -- and then have manychat takeover after they engage the default chat bot.

I am having problems though,  with manychat taking over after they talked to my facebook ‘default template’ , I’ve used the “user sends a message” … and its not working too well.

any better ways to do this? id prefer to use the above objective