Modbus server error when connection to Fogwing

Hi,
Im new to IoT and node-Red.
working step-by-step by this instructions link and still having an error:
[error] [modbus-flex-write:write Modbus payload] Error: Modbus exception 4: Slave device failure (device reports internal error)

could anyone please check are these instructions correct?

at the same time having also problems with MQTT.fx

2023-04-28 14:26:45,844 INFO --- ScriptsController : Clear console.
2023-04-28 14:26:45,845 ERROR --- BrokerConnectService : MqttException
2023-04-28 14:49:08,318 INFO --- BrokerConnectorController : onConnect
2023-04-28 14:49:08,319 INFO --- ScriptsController : Clear console.
2023-04-28 14:49:08,322 INFO --- MqttFX ClientModel : MqttClient with ID 1151-3365-2373-3077 assigned.
2023-04-28 14:49:09,136 ERROR --- MqttFX ClientModel : Error when connecting

is it correct that according to Node red instruction the port is 1883 and in MQTT instruction using 8883?

Thank you very much

anyone who could help?