Structuring a Multi-Page App Not Updating values

Tried to run “Structuring a Multi-Page App” example form And the value is not updated throught the app1 callback.

@app.callback( Output('app-1-display-value', 'children'), [Input('app-1-dropdown', 'value')])

def display_value(value): return 'You have selected "{}"'.format(value)

From similar posts, I tried including all callbacks in the file where app is initialised (, and it worked. However, just want to check if the example structure could work, since it is more organised.