Is anyone experiencing the same issue as me? I'm trying to integrate Facebook Page messages into my system, but when setting up the webhook on the Facebook Developer app screen, it doesn't allow me to test sending API messages to the webhook. Unlike other APIs where clicking 'test' opens a popup to send the API, I receive data into my system. However, when I click 'test message', it only opens a blank page. I've tried activating the Facebook Developer app and connecting the page, but I don't receive any response on the webhook, whereas on the Facebook Developer website, I still receive everything except 'message'.