This is the only user information currently available through the chat API, and you cannot use any other API to request user information, because the User ID (sender ID) that we receive on our website is only for for the App area, the Page is completely different from the actual Facebook UserId, and there is currently no way to link the two identifiers.
You can ask the user to log in using the FB login API and link the two identifiers at the end, but that would not be the ideal way to do this.
Edit: 2016-07-26
Facebook has introduced a new feature for the Messenger platform called Link Account . This can be used to identify the user who created the account on your website through Facebook Login . Logging into Facebook has its own set of permissions, which you can use to get more information using the Facebook graphical API. You can find the full list here .
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