Django Model Exception on Pre-existent Database: Cannot resolve keyword 'user' into field. Choices are: organization_id

I'm currently building Django model classes for an already existing database. We have three tables: Organization, User, and UserOrganizationMap. This is because there is a Many-to-Many relationship between the tables Organization and User (a user can belong to multiple organizations and an organization has multiple users). I had to explicitly create the UserOrganizationMap model class since it exists in the database already and I cannot use the one that would be created by Django. This is the code to create those models:

This the code to create those models:

class Organization(models.Model):
    organization_id = models.UUIDField(primary_key=True)
    organization_name = models.TextField()

    class Meta:
        app_label = 'myapp'  # each model will require this
        managed = False
        db_table = 'organization'
class User(models.Model):
    user_id = models.UUIDField(primary_key=True)
    user_name = models.CharField()
    organizations = models.ManyToManyField(
        to=Organization,
        through='UserOrganizationMap',
        through_fields=('fk_user', 'fk_organization'),
    )

    class Meta:
        app_label = 'myapp'  # each model will require this
        managed = False
        db_table = 'user'
class UserOrganizationMap(models.Model):
    fk_user = models.ForeignKey(
        User, on_delete=models.CASCADE, db_column='user_id',)
    fk_organization = models.ForeignKey(
        Organization, on_delete=models.CASCADE, db_column='organization_id',)

    class Meta:
        app_label = 'myapp'  # each model will require this
        managed = False
        db_table = 'user_organization_map'

When I tried to iterate over the users I get the following Error

users = User.objects.all()
for user in users:
    print(user.user_id)
    print(user.organizations.all())

django.core.exceptions.FieldError: Cannot resolve keyword 'user' into field. Choices are: organization_id, organization_name, 
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