Cannot “Select Facebook Page” to proceed with setup

I’ve downloaded and activated the FB messenger plugin for my WP installation, but when I click on “Select Facebook Page,” nothing drops down or otherwise appears. I am the administrator for the FB page that I intend to have the messages sent through from my site, so I’m not understanding why no FB page shows in what’s supposed to be the dropdown. I’m using Plugin version 2.5, just downloaded from WP plugin area.

Thanks.