Facebook Messenger account linking is not working

[onejgordon]

• Some users are not getting any response from Messenger Flow chatbot
• Others are unable to link their account.

In the second case, the login prompt appears in chat, but when clicked, a dialog opens on a Flow authentication page, but without a redirect_uri parameter in the query string, which raises an exception upon successful authentication.

This was previously working, so it may be a Facebook API change that broke this integration flow.