The documentation for the Facebook Messenger API points out how to setup your initial bot webhook. I just committed a quick patch that would make it very easy to setup a quick script to get it done using the unreleased and still in progress Perl’s Facebook::Messenger::Bot:
useFacebook::Messenger::Bot;
use constant VERIFY_TOKEN => 'imsosecret';
my $bot = Facebook::Messenger::Bot->new(); # no config specified!$bot->expect_verify_token( VERIFY_TOKEN );
$bot->spin();
This should get you sorted. What endpoint would that be, though? Well that depends on how you’re giving Facebook access to your Plack’s .psgi application.