I can't sync Flow, when I activate it says it couldn't find any other computer. I have already checked the points below and they are correct. What can it be?

Make sure your mouse appears in Options+ on all computers.
Make sure your computers are connected to the same network.
Make sure the Options+ communication channel is not blocked by any firewall or antivirus applications.
Make sure your internet connection is working.
Make sure you have Flow enabled on all computers.