I had a look at . | Fibery
It’s a perfectly fine API, but why would you call it a REST API?
It’s a classic RPC API: there is one endpoint /commands, to which you POST batches of datalog-style code.
Though it’s true that REST is mostly used rather loosely on the web today, it does have a defined meaning. At its most basic, I’d say it means “not RPC” 
I recommend calling it an RPC API. This correctly characterizes the design and helps to correctly set expectations.