MQTT : Failing to receive "service/data"

I have installed an application called “MyMQTT” on my Android Smartphone and I have subscribed to receive MQTT notifications coming from TTN. When my device is connected or send a message, I do receive notifications for :
v3/my-mqtt-test-app@ttn/devices/eui-0080e115000ac6ed/join
v3/my-mqtt-test-app@ttn/devices/eui-0080e115000ac6ed/up

However, I don’t receive anything for
v3/my-mqtt-test-app@ttn/devices/eui-0080e115000ac6ed/service/data

Would you know why?

The “up” notification contains all the data I want but I’m looking for a way to get ONLY the payload data (the same payload data as what is visible on TTN console when I select the device, click on “Live data” and then click on “Forward Uplink Data Message”. The payload data is displayed on the same line).

Thank you

I have just seen that my need is in fact the same as: Only Reading the Payload Fields in MQTT - Gateways / TTKG - The Things Kickstarter Gateway - The Things Network

That means you know the answer to you question…