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First of all, you need to create a Facebook Application in the developers page. You will get a Facebook app code and a secret.
For using the /rest-auth/facebook/ method from the django-rest-auth, you need to send the access code (obtained using the javascript SDK) and the code of the Facebook Application.
Finally, before using this method, you have to go the the application back-office and create a social application, using the Facebook app code and the secret.
Source:stackexchange.com