Mqtt broker app communication with local client event based script

[Rajesh]

broker = "localhost"
port = 1883
username = "admin"
password = "password"
topic = "casambi/1/set/target_level"

value = event.getvalue()

if value == 1
  then
  topic = "casambi/1/set/target_level"
payload = tostring"("level":255,"duration":1,"targetid":177,"targettype":1,)"
else
  payload = tostring"("level":0,"duration":1,"targetid":177,"targettype":1,)"
  end
 
mqtt = require("mosquitto")
client = mqtt.new()

client.ON_CONNECT = function(status, rc, msg)
  if status then
    log("mqtt connected")
    client:publish(topic, tostring(payload))
  else
    log("mqtt connect failed " .. tostring(msg))
    client:disconnect()
  end
end

client.ON_PUBLISH = function()
  client:disconnect()
end

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

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

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Error log shows:
attempt to call global 'level' (a nil value)
stack traceback: