The relay feature has been retired since early this year. It’s partly because very few users are actually using this feature, and those who do can use an external 24VAC relay instead. A while back I wrote a blog post about using 24VAC relay with OpenSprinkler:
https://opensprinkler.com/using-24v-ac-relays-with-opensprinkler/
In addition, for controlling powerline devices, you can use the RF station feature in conjunction with off-the-shelf RF remote power sockets, which are easier and safer to work with than relays.