Hi, this is what I added into my telegraf.conf file , if any help with your issue
[[inputs.mqtt_consumer]]
servers = ["tcp://eu1.cloud.thethings.network:1883"]
qos = 0
connection_timeout = "30s"
topics = [ "v3/bal@ttn/devices/+/up" ]
client_id = "telegraf"
username = "bal@ttn"
password = "NNSXS.***********************************LQ"
data_format = "json"