I have send variable (waterlevel) by ESP8266 to Ubidots and read it successfully. But I have PLC in other place I need to receive waterlevel by PLC how can I do this, knowing that I was sent some variables successfully from PLC to Ubidots via KEPOPCServer and MQTT.
Greetings, you should implement a GET request at your device to retrieve the value from Ubidots. Ubidots will always return the value as decimal, so at your ESP8266 side you should parse it to bytes and send it to your PLC through RTU or Modbus that are the common communication industrial protocols that usually manage a PLC.
All the best