Downlink message via TTN to Lorawan device

Setup, Configuration and Use Runtime
1

Openhab 5.0
Hello again
I started to play with Lorawan devices and installed the trackerD from dragino using TTN. I get all messages from trackerD which is time, location and temperature. When pressing the red button the alert comes in and will be repeated 60 times.
I‘d like to stop the alert message by sending 0x0201 via mqtt as a downlink message to TTN.
The command topic is

v3/xxxxxxx@ttn/devices/xxxxx/down/push

Can anybody help me to configure the payload.

2

Just for information, if someone needs it later on.
The command ‘0x0201’ needs to be BASE64 coded, which results in ‘AgE=’

I use a script with the content


items.TrackerD_stopAlarm.sendCommand("{ \"downlinks\": [ { \"f_port\": 1, \"frm_payload\": \"AgE=\",  \"priority\": \"NORMAL\" } ] }");