Puck js, how to send MQTT message with button pressed?

Hello
Amazing! the button works fine. Thank you very much.
I'm trying to get some feedback information back to puck, like LED.
When I send: /ble/write/e7:e0:57:ad:36:a2/nus/nus_tx (with my address obviously) I get en error:

MQTT>/ble/write/c9:a2:6b:fd:3f:9d/nus/nus_tx => "LED1.set();\n"
Service 6e400001b5a3f393e0a9e50e24dcca9e Characteristic nus_tx
Error Connecting: Error: Command Disallowed

Any clue what is wrong please?