You can toggle the pin by connecting to the master website and clicking the button. You would have to add some handshaking or something if you want to add more slaves. This works very reliably though for me so far with very little lag on v3 a39.
master code:
memclear
wifiapsta
udpbegin 8081
let data = 0
let stat = "OFF"
wprint "Status = "
wprint htmlvar(stat)
wprint "<br>"
button "Toggle Relay", [doit]
timer 500, [read]
[doit]
if data = 1 then let data = 0 else let data = 1
udpwrite "192.168.0.109", 8082, str(data)
wait
[read]
let stat = udpread()
wait
slave code:
memclear
udpbegin 8082
let stat = "OFF"
timer 500,[doit]
wait
[doit]
let rec = val(udpread())
io(po,2,rec)
if rec = 1 then let stat = "ON" else let stat = "OFF"
udpwrite "192.168.0.102", 8081, stat
wait