Hello Claudia,
your code works perfectly fine. Just copied it to my Eclipse (public static main method). Of course I used my tokens and IDs and a message. In a console I see the following output: {"msg":"1 message(s) received from device [5bded13c-7137-43ab-9091-434e14f62b24]"}
Could you please re-check you java console output?
Regards,
Anton