I copied and pasted into console and in game exactly as you have it in the directions and changed the name, command and cost for my server.   When I use the in-game commands - it keeps saying I need to set a rewards cost even though I already set it.

When I use the F1 console commands, it doesn't give any confirmation nor any error message but when I then go to the shop there are no commands set up.

Rust Console 4.0
> rewards add command "blackvenomeasy" "/bv 0" <25>
> rewards add command "blackvenomhard" "/bv 1" <75>
Saved 0 banks
> rewards add command "blackvenomelite" "/bv 2" <100>
Saved 0 banks
Saved 0 banks