Execute a command on device over serial connection with Plink

Question

This is the first time that I am trying to write a "plink" command that will connect to a device and to have a remote command executed afterwards. And I am blocked so far.

Here is the command I have tried.

plink -v device ( execute shell; whoami)

I was expecting the full command process finished right away, but somehow, it hangs. here is the screenshot after I have run the above command,

plink -v device ( execute shell; whoami) 
Opening serial device COM1
Configuring baud rate 115200
Configuring 8 data bits
Configuring 1 data bits
Configuring no parity
Configuring XON/XOFF flow control

And after i have pushed the extra "Enter" key from my keyboard, then I see the popup of device name, which means the connection part is ready,

plink -v device ( execute shell; whoami) 
Opening serial device COM1
Configuring baud rate 115200
Configuring 8 data bits
Configuring 1 data bits
Configuring no parity
Configuring XON/XOFF flow control

FX04DN4N16000408  #

What I don't understand is why do I need to run this extra manual step ?

Thanks,

Jack