The Modbus slave from the FAQ Modbus Communikation Master/Slave via Ethernet is used here.
Insert an Ethernet adapter in the device tree and specify the interface to be used.
If a target system is not defined yet, then the error message "Gateway not configured" is displayed.
Insert a Modbus TCP Slave below the Modbus TCP Master in the device tree.
Pay attention that the address is the the same as for the Modbus Slave Device.
Adapt the POU PLC_PRG as follows:
Resetting to an invalid IP address is not possible.