Lorawan - The Things Network - Dragino sensor PS-LB

[clue9]

Hi. 
I had a need for a remote sensor to monitor the waterlevel in a well in the forest 200m from house uphill with terrain in the way from the house, and ended out with a lorawan sensor from Dragino (PS-LB model)
Have it communicating to the things network now and gets the payload decoded by a code i got from draginos websites in the TTN console. But in MQTT explorer it seems like every package is formatted in a .json format in one topic and not with the decoded data as separate topics to subscribe to. 
here is a copy paste the end topic (v3/sensor-well-level@ttn/devices/eui-xxxxxxxxxxxxxxxx/up) from MQTT explorer.

Code:

{
  "end_device_ids": {
    "device_id": "eui-xxxxxxxxxxxxxxxx",
    "application_ids": {
      "application_id": "sensor-well-level"
    },
    "dev_eui": " xxxxxxxxxxxxxxxx ",
    "join_eui": " xxxxxxxxxxxxxxxx ",
    "dev_addr": "xxxxxxxx"
  },
  "correlation_ids": [
    "gs:uplink:01HH0xxxxxxxRX9DMMXWT5XMN"
  ],
  "received_at": "2023-12-06T23:01:24.067287960Z",
  "uplink_message": {
    "session_key_id": "AYwxx9WcxkxxxFh5xxeYZg==",
    "f_port": 2,
    "f_cnt": 573,
    "frm_payload": "DO4ABSM+AAAA",
    "decoded_payload": {
      "Bat_V": 3.31,
      "Exti_pin_level": "Low",
      "Exti_status": "False",
      "IDC_intput_mA": 9.022,
      "IN1_pin_level": "Low",
      "IN2_pin_level": "Low",
      "Probe_mod": 0,
      "VDC_intput_V": 0,
      "Water_deep_cm": 156.938
    },
    "rx_metadata": [
      {
        "gateway_ids": {
          "gateway_id": "tos-loragw-03-bjolab-net",
          "eui": "3133303719004900"
        },
        "time": "2023-12-06T23:01:23.822356Z",
        "timestamp": 106957004,
        "rssi": -104,
        "channel_rssi": -104,
        "snr": 6.5,
        "location": {
          "latitude": 69.655554,
          "longitude": 18.919952,
          "altitude": 80,
          "source": "SOURCE_REGISTRY"
        },
        "uplink_token": "CiYKJAoYdG9zLWxvcmxxxxxxYWItbmV0EggxMzA3xxxxxxxxxw/rDqwYQ1u6zmAMg4LmJuY6A+wE=",
        "channel_index": 6,
        "received_at": "2023-12-06T23:01:23.856487766Z"
      },
      {
        "gateway_ids": {
          "gateway_id": "tos-loragw-02-bjolab-net",
          "eui": "313330371A006500"
        },
        "time": "2023-12-06T23:01:23.823376Z",
        "timestamp": 1786967500,
        "rssi": -103,
        "channel_rssi": -103,
        "snr": 3,
        "location": {
          "latitude": 69.661456,
          "longitude": 18.93894,
          "altitude": 111,
          "source": "SOURCE_REGISTRY"
        },
        "uplink_token": "CiYKJAoYdG9zLWxxxxxxxxxYWItbmV0EggxMzA3GgBlAxxxxxxxxxxMCMP6w6sGEKKwzZsDIODJwPyAjYcC",
        "channel_index": 6,
        "received_at": "2023-12-06T23:01:23.863197218Z"
      },
      {
        "gateway_ids": {
          "gateway_id": "tos-loragw-01-bjolab-net",
          "eui": "3133303722003D00"
        },
        "time": "2023-12-06T23:00:42.527271Z",
        "timestamp": 1961777188,
        "rssi": -111,
        "channel_rssi": -111,
        "snr": -7,
        "location": {
          "latitude": 69.67219385058512,
          "longitude": 18.96223068237305,
          "altitude": 110,
          "source": "SOURCE_REGISTRY"
        },
        "uplink_token": "CiYKJAoYdG9zLxxxxxxxxxxItbmV0EggxMzA3IgA9ABCkxxxxxxxxxMP6w6sGEIxxxxxwDIKCZoZiMkocC",
        "channel_index": 6,
        "received_at": "2023-12-06T23:01:23.864463746Z"
      }
    ],
    "settings": {
      "data_rate": {
        "lora": {
          "bandwidth": 125000,
          "spreading_factor": 7,
          "coding_rate": "4/5"
        }
      },
      "frequency": "867700000",
      "timestamp": 106957004,
      "time": "2023-12-06T23:01:23.822356Z"
    },
    "received_at": "2023-12-06T23:01:23.857527261Z",
    "consumed_airtime": "0.056576s",
    "locations": {
      "user": {
        "latitude": 69.691434,
        "longitude": 18.7124573,
        "altitude": 47,
        "source": "SOURCE_REGISTRY"
      }
    },
    "network_ids": {
      "net_id": "000013",
      "ns_id": "EC65xxxxxxxx0181",
      "tenant_id": "ttn",
      "cluster_id": "eu1",
      "cluster_address": "eu1.cloud.thethings.network"
    }
  }
}

I need to get subscribed to new updates (each 20 minutes) for the data of interest, (se below snippet of the above where i add double ## in front to mark the interest) and send it to group adresses in my LM, one value to KNX ( "Water_deep_cm" ).

Someone here who could help as i see this involves .json and doble encoding and all this [ and { parts making me as a newbe lua guy confused how to sort this out.
MQTT server is 
eu1.cloud.thethings.network:1883 and i have to supply a username and a password i get from TTN to connect as a client.

Code:

##"received_at": "2023-12-06T23:01:24.067287960Z",
  "uplink_message": {
    "session_key_id": "AYwxx9WcxkxxxFh5xxeYZg==",
    "f_port": 2,
    "f_cnt": 573,
    "frm_payload": "DO4ABSM+AAAA",
    "decoded_payload": {
      ##"Bat_V": 3.31,
      "Exti_pin_level": "Low",
      "Exti_status": "False",
      ##"IDC_intput_mA": 9.022,
      "IN1_pin_level": "Low",
      "IN2_pin_level": "Low",
      "Probe_mod": 0,
      "VDC_intput_V": 0,
      ##"Water_deep_cm": 156.938
    },

[admin]

Create a resident script with non-zero sleep time. Modify username, password and topicname variables as needed. Change group addresses in the ON_MESSAGE callback.

Code:

broker = 'eu1.cloud.thethings.network'
port = 8883
username = 'PUT_USER_HERE@ttn'
password = 'PUT_API_KEY_HERE'
topicname = 'v3/sensor-well-level@ttn/devices/eui-xxxxxxxxxxxxxxxx/up'

require('json')
mqtt = require('mosquitto')
client = mqtt.new()

client.ON_CONNECT = function(status, rc, msg)
  if status then
    log('mqtt connected')
    client:subscribe(topicname)
  else
    log('mqtt connect failed ' .. tostring(msg))
    client:disconnect()
  end
end

client.ON_MESSAGE = function(mid, topic, payload)
  local data = json.pdecode(payload)

  if type(data) ~= 'table' then
    return
  end

  local datetime = data.received_at
  local sensor = data.uplink_message.decoded_payload

  grp.checkwrite('1/1/1', datetime)

  grp.checkwrite('1/1/2', sensor.Bat_V)
  grp.checkwrite('1/1/3', sensor.IDC_intput_mA)
  grp.checkwrite('1/1/4', sensor.Water_deep_cm)
end

client.ON_ERROR = log

client:login_set(username, password)
client:tls_insecure_set(true)
status, rc, msg = client:connect(broker, port)

if status then
  client:loop_forever()
else
  log('connect failed: ' .. tostring(msg))
end