@jmahesh You are connecting to GATT Server as client, so what you can do is request the server send you notifications. You can't send notifications as a client. Bluetooth.PROP_NOTIFY means you can request notifications on that characteristic. I'm guessing that characteristic is not writable (read only) hence you get that error? If what you want is to be notified by the Server (e.g. when the value changes) use the char.callback(trigger=Bluetooth.CHAR_NOTIFY_EVENT, handler=YourHandlerFunct, arg=YourOptionalArgument)

please add time.sleep after connection and make service as dictionary, things will work...

@berni I don't know if the bug was solved in new firmware releases, You should try the same code on the 1.4.0.b1 version, maybe it'll solve your problem.