No data available in bucket using Telegraph

I am struggling with getting data into a bucket (Influx cloud2) from The Things Network using Telegraph and the MQTT-plugin. I have followed the instructions provided in this link.

I assume some parts are wrong in the configuration:

 data_format = "json"
 json_query = "uplink_message"
 json_string_fields = ["frm_payload"]

I have also used [“fm_payload”] and [“decoded_payload”] but without any result.
Telegraph is running on a Raspberry Pi. What could possibly be wrong?

Kind regards,