title: TypeError: add() argument after * must be a sequence, not Subscribers
body: <pre><code>class Subscribers(User):
      date = models.DateField()
      user = models.OneToOneField(User)
  
  class Tour(models.Model):
      owner_id = models.ForeignKey(User)
      name = models.CharField(max_length=50)
      location = models.ManyToManyField(Location)
      subscribers = models.ManyToManyField(Subscribers, related_name="sub")
  </code></pre>
  
  <p>I am trying to do this in another file:</p>
  
  <pre><code>user1 = User.objects.create_user('John','j@j.com','j1')
  user2= User.objects.create_user('Mike','m@m.com','m1')
  user3= User.objects.create_user('kokoko','m@m.com','m1')
  user4= User.objects.create_user('lalal','m@m.com','m1')
  sub = Subscribers()
  tour = Tour()
  tour.id = "1"
  tour.name = "hello"
  tour.owner_id = user1
  tour.subscribers = sub
  </code></pre>
  
  <p>but I have this error:
  TypeError: add() argument after * must be a sequence, not Subscribers </p>