getting this error 'AttributeError: 'str' object has no attribute 'get_balance_f' on my rest api

Im making a rest api so I can communicate with my python script that does requests to a website and gets the data from the website.

class Classroom():
    def __init__(self, numbercard, password) -> None:
        self.session = requests.Session()
        self.school = 400786
        self.numbercard = numbercard
        self.password = password
        self.logged_in = False


        def login(self):
        payload = {
            'modo': 'manual',
            'escola': '400786',
            'nrcartao': self.numbercard,
            'codigo': self.password,
        }

        res = self.session.post('http://giae.esars.pt/cgi-bin/webgiae2.exe/loginv2', 
        json=payload)

        self.logged_in = res.ok

        def get_balance_f(self):
        balance_request = self.session.get('http://giae.esars.pt/cgi- 
        bin/webgiae2.exe/saldo')
        balance_json = balance_request.json()

        
        self.balance = balance_json['saldo']
        
        print(balance_json['saldo'])

this is one part of my python scrip that logins into the website and gets how much money i have in my school card.

from flask import Flask, request
from classroom import Classroom
from random import choice

chars = [
'q',
'w',
'e',
'r',
't',
'y',
'u',
'i',
'o',
'p',
'a',
's',
'd',
'f',
'g',
'h',
'j',
'k',
]

app = Flask(__name__)

def generate_id() -> str:
    return ''.join(choice(chars) for _ in range(8))

@app.route('/login', methods = ['POST', 'GET'])
def login_receive():
    card_number = request.json['username']
    password = request.json['password']
    user = Classroom(card_number, password)
    user.login()
    if user.logged_in:
        uid = generate_id()

        return {'message': 'Login succesful', 'uid':uid}
    else:
        return {'message': 'Login failed'}
    

    @app.route('/classroom/myinfo', methods=['GET', 'POST'])
    def myinfo():
    user = request.headers['uid']

    return user.get_balance_f()

on this code the login part is working, but when i tried to send a get request i get this error 'AttributeError: 'str' object has no attribute 'get_balance_f', and i dont get it.