User attendance in app

Hi, i try to create list of users attendance in goal app.

But i don't know how to filter user.

I have Goal model:

class Goal(models.Model, Activity):
    title = models.CharField(max_length=255, verbose_name='Tytuł')
    image = ImageField(blank=True, verbose_name='Tło')
    body = HTMLField(verbose_name='Treść')
    tags = TaggableManager()
    created_at = models.DateTimeField(auto_now_add=True)
    author = models.ForeignKey(User, on_delete=models.CASCADE)
    slug = AutoSlugField(populate_from='title')

and Joined model:

class Joined(models.Model, Activity):
    goal = models.ForeignKey(Goal, on_delete=models.CASCADE, related_name='joined')
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='joined_users')
    created_at = models.DateTimeField(auto_now_add=True)
    joined = models.BooleanField(default=False)

I try:

def goalusers(request, slug):
    goal = get_object_or_404(Goal, slug=slug)

    users = goal.joined_users.all()

    return render(request, 'goals/users.html',
                {'goal': goal,
                'users': users})

This makes error: 'Goal' object has no attribute 'joined_users'.

I try also:

users = User.objects.filter(joined_users__joined__in=goal)

but then error is:
'Goal' object is not iterable.