I cant pass a variable in pyrebase, even though it has the string form

Question

Im making a game in python and i want to save the high score of a certain account to firebase. However, this code doesnt work, unless instead of writing f'{username}', i write the name i want (for example "gamer123"). Also, the set part isnt being recognized as json.

def signup():
global high_score
layout1=[
[ps.Text("Username: "), ps.Input(key="username", do_not_clear=False)],
[ps.Text("Password: "), ps.Input(key="password", password_char="*", do_not_clear=False)],
[ps.Button("Signup")]
]
janela=ps.Window("Signup", layout1)
while True:
    eventos,valores=janela.read()
    if eventos==ps.WINDOW_CLOSED:
        break
    if eventos=="Signup":
        username=valores["username"]
        password=valores["password"]
        try:
            user=auth.create_user_with_email_and_password(username, password)
            ps.popup("Account created successfully!")
            janela.close()
            db.child('Users').child(f'{username}').set(f'{{"high score": {high_score}}}')
            menu()
            
        except:
            janela.close()
            ps.popup("Username already exists!")