Hello to everyone in forum!

I was wondering if somebody with some expertise with modbus protocol and siemens could help me with this. 

I have been working in a project in which I require to control 4 differents VFD (Danfoss FC 51 Drive) trough Modbus Protocol.

I'm working with modbus RTU in a S7-1215C PLC.

I already have acces to each one of these VFD and I can turn on/off the motors and also change the speed. The problem is that the buttons that sends this commands to the VFD doesn't work all the time. I mean, if the button is pressed 10 times, maybe it sent the command to the VFD only 3 times.

I suppose that there should be a way to verify that the command has been sent, the VFD receive it and the operator doesn't have to press the button so many times. There's  a way to do this?

What I have now  as can be seen in the attached picture is that when the operator press M5.6 button, all that is configured on the modbus communication block is sent during three seconds to the VFD, but how can I verify that the VFD really receives that and execute it?

The code is programmed in the same way for each VFD, to change speed and to turn it on or off. 

I count on you.

Best Regards!