@npocmaka Thanks
I ended up using msg.exe but because of restrictions on our company's network I used a combination of psexec and msg
msg server:IPADDRESS /v "message"
didn't work so I used
psexec \IPADDRESS -u username -p password msg /server:IPADDRESS /v "message"
but in order for it to work I had to run
psexec \IPADDRESS -u username -p password reg add "HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server" /v AllowRemoteRPC /t REG_DWORD /d 1 /f
on the remote computer. I got the reg command from another post in StackOverflow actually!