Understanding sqlalchemy Foreign Keys

I wrote a method for registering data using sqlalchemy, but
Error setting foreign key.

In addition, the Belong class id is called as a foreign key in the Page class.

▼ I want to be able to POST.* GET: I was able to retrieve data
a.py 一部Partial excerpt

class PageRepository():
    def__init__(self, url):
        engine=create_engine(url)
        #Base=declarative_base()
        Session=sessionmaker (bind=engine)
        self.session=Session()

    # page registration
    def post(self, title, belong_id):
       now_time = datetime.now()
       page=Page(id=null, title=title, Belong_id=belong_id, created_at=now_time, updated_at=now_time)

       self.session.add(page)
       self.session.commit()

page_repository=PageRepository(access_point)
page_repository.post('flask test',1)

→ python a.py results in an error.

Error

sqlalchemy.exc.NoReferencedColumnError: Could not initialize target column for ForeignKey 'belong.id' on table 'page': table 'belong' has no column named 'id'

b.py 一部Partial excerpt

engine=create_engine(access_point, echo=True)
Base=declarative_base()

class Belong (Base):
    __tablename__='belong'

    id=Column('belong_id', Integer, primary_key=True)
    # pages = relationship ('Page', backref="belong.id")
    pages=relationship('Page')

Base.metadata.create_all(engine)


Class Page (Base):
    __tablename__='page'

    id=Column('page_id', Integer, primary_key=True)
    title=Column('title', String(200))
    belong_id=Column('belong_id', Integer, ForeignKey('belong.id', onupdate="CASCASE',ondelete="CASCASE"))
    created_at=Column(DateTime)
    updated_at=Column(DateTime)

Base.metadata.create_all(engine)

I checked many things, but I didn't know...
I would appreciate it if you could tell me how to check.
Thank you for your cooperation.