title: Django REST: Problem with AUTH_USER_MODEL importing
body: <p>I'm following <a href="https://krakensystems.co/blog/2020/custom-users-using-django-rest-framework" rel="nofollow noreferrer">this tutorial</a> and trying to create custom user for REST-API. </p>
  
  <p><strong>settings.py:</strong></p>
  
  <pre class="lang-py prettyprint-override"><code>INSTALLED_APPS = [
      # blah blah
      'courses',
  ]
  
  AUTH_USER_MODEL = 'courses.CustomUser'
  </code></pre>
  
  <p>I have</p>
  
  <blockquote>
    <p>django.core.exceptions.ImproperlyConfigured: AUTH_USER_MODEL refers to model 'courses.CustomUser' that has not been installed</p>
  </blockquote>
  
  <p><strong>project tree:</strong></p>
  
  <pre><code>- django-project
      - courses
          - models.py
  </code></pre>
  
  <p><strong>models.py:</strong></p>
  
  <pre class="lang-py prettyprint-override"><code>class CurstomUser(AbstractBaseUser):
      username = None
  
      first_name = models.CharField(max_length=20)
      last_name = models.CharField(max_length=20)
      email = models.EmailField(max_length=254, unique=True)
  
      objects = CustomUserManager()
  
      USERNAME_FIELD = 'email'
      REQUIRED_FIELDS = [USERNAME_FIELD, 'first_name', 'last_name']
  
      role = models.CharField(max_length=2, choices=UserRole.choices, null=False)
  
      def __str__(self):
          return '{} {}'.format(self.first_name, self.last_name)
  </code></pre>
  
  <p>What's the problem? It seems I've set up <code>AUTH_USER_MODEL</code> correct way</p>