Modbus network commands: Read/write to modbus subnet device over RTU

Yes, I have try multiple value, I also read this post Using the T3-BB controller to read & write to modbus tcp & BACnet/IP sensors - #5 by DonatoM
The module have 2 relay.

The command turn relay 1 on:

02 05 00 00 FF 00 8C 09

8C 09 is CRC
The command turn relay 1 off:

02 05 00 00 00 00 CD F9

CD F9 is CRC

  • 02 is address of the module on the Modbus
  • 05 I guest is write single coil command
  • Byte 3 and 4 is the relay, 00 00 is the relay 1. 00 01 is relay 2
  • Byte 5 and 6 is on/off command: 00 00 for off and 00 FF for on.

So it is 64 bit but, I read that your app only support 16, If you have experience please help me in detail, I take days and could not make it work.