I have this same problem. It used to work fine, but now it does not, and I have no idea why. I've walked through everything that seems could possibly be preventing it from working, to no avail. Pulseway simply says "Wakeup command failed" and nothing happens.
Yes, I've opened port 9, I've done it all (including some of the things suggested which are not necessary at all). I have not "undone" anything I initially set up to get it working in the first place. But between the time it worked and now, I have updated my router's firmware, my Ethernet adapter driver (I believe), and of course many Windows updates, which are reknowned for breaking things.
I have no idea, but it's frustrating, especially now that I can't wake up my PC with the keyboard or mouse anymore (due to the use of a USB switch).