Please see my attached flow and guide where I did mistake.
When I write data into Modbus server through inject node then it write on Modbus server,
But when I try to write data of MQTT then its not write on Modbus.
Both have same output Format(msg.payload : array[51])
Add a debug mode showing what you are sending to the server node. Click the inject node and then trigger the mqtt input and show us what you see for each case.