This can happen if the code is expired. They expire pretty quickly by default. You can look up your code in the Django admin under Grants and change the expiration date to far in the future.
原因：
Django OAuth Toolkit 默认的Grant过期时间非常短暂。
参考资料：
http://stackoverflow.com/questions/27056272/django-oauth-toolkit-invalid-grant-error
【Web】Django OAuth invalid_grant error
原文：http://www.cnblogs.com/junneyang/p/5502090.html