RFtoy communicates with RF power sockets like these:
https://www.amazon.com/Etekcity-Wireless-Electrical-Household-Appliances/dp/B0087EIDRS
it’s not for WiFi power sockets like sonoff. If sonoff has a public HTTP API, you can actually use OpenSprinkler’s HTTP station feature to send command to sonoff to turn it on/off.
It used to be that RF power sockets are much cheaper, because you can often get a packet of 3 for like $20. But these days, with sonoff, the WiFi power sockets are quickly becoming extremely cheap, so RF power sockets are being made obsolete…