The App Token is needed for us to configure webhooks automatically so that you don’t need to do it manually.
Find your App Token on Meta for Developers
Go to
http://developers.facebook.com > Tools.
Find
Access Token Tool in a dropdown menu or press View All Tools to browse for it.
Copy your App Token.
If you have several apps, make sure to copy the right token for the app associated with WhatsApp Business.
Add App Token to Chat
Copy the App Token into the required field on the IM Integration page.