If you're looking for statically typed FP, honestly, start with Elm. You can do it in a weekend it's so conceptually contained. Then F# and OCaml are highly regarded. Avoid Haskell - worst bang for your buck on seeing returns on learning. It has some interesting concepts, but is a terrible language for learning statically typed functional programming.

If you're looking for dynamically typed FP (ex. LISP), go with Clojure, or lesser rec possibly Racket flavor of Scheme.