Can't get gamerule to work in my server

I started up an MC PE server, using the plugin version. I have a few plugins on it relating to permissions. I am OPed on the server and have the "owner" status on the permissions plugin, which in the coding has all of the "essential" commands enabled. I tried both on the console and in-game to change the keep inventory gamerule to true, but both in console and in game it said it didn't recognize the command. I typed in "/gamerule keepInventory true". When I typed /help to get a list of commands on the console, it wasn't even listed as a command. Any ideas on why it wouldn't work? Thank you!

Alright, thank you. We ended up playing on a non-plugin server in the end because the world generation was pretty weird (no mobs, treeless swamp, etc).