Sometimes when you send message in a facebook channel, you will encounter problems like screenshot below
This happens because several reasons:
a.The token expired every 3 months
b.Your FB page's Admin account changed password
c.Other security reasons that FB deems as neccessary to reset token.
Here are the steps to reconnect your FB Page.
1.Open Integration>Facebook Messenger. Click Settings on the channel that you will reconnect
2.You will meet the setting page of the channel. Click reconnect.
3.Skip to step 5 if you have logged in, if not yet the FB Login popup will open. Input the email and password of FB Account that's an Admin the FB Page that you want to reconnect.
4. At the next page, Click Edit Settings, Choose page that you want to reconnect and click next, on the next page choose all permission and click Done. After finishing, click OK.
5.The system will ask you to Continue after already login like screenshot below. Click Continue.
6.After that, the reconnecting is finished. You can send message again.