Did you make sure the string decoder ran?

You need to provide coercion

Hmm. I think I’m properly providing coercion, but maybe I’ve misconfigured it or something. Under (ring/router _ {options}, I have

:coercion   (reitit.coercion.malli/create
                          {;; set of keys to include in error messages
                           :error-keys       #{#_:type :coercion :in :schema :value :errors :humanized #_:transformed}
                           ;; schema identity function (default: close all map schemas)
                           :compile          mu/closed-schema
                           ;; strip-extra-keys (effects only predefined transformers)
                           :strip-extra-keys true
                           ;; add/set default values
                           :default-values   true
                           ;; malli options
                           :options          nil})

e.g. when I print the data in my ring handler, the enum fields I defined in malli are coming up as #object[clojure.lang.AFunction$1 0xe1da5b0 "clojure.lang.AFunction$1@e1da5b0"] and so on - looks like the coercion isn’t being applied. I have just tried to explicitly set the coercion in the route in question as well (i.e. like this:

:post    {:name ::create-foo
          :coercion reitit.coercion.malli/coercion
          :handler    h/create-foo!
          :parameters {:body requests/foo}
          :summary    "Create a new foo."}}]

I think it may be that my enums are not being transformed. I can see how to add a transformation to a direct malli/decode call (e.g. (m/encode int? 42 mt/string-transformer) , as per documentation at https://github.com/metosin/malli#value-transformation, but I’m not sure how to define such a transformation as part of my ring spec. I think I’m getting there but I’m not there yet!

I sorted this out. As with so many problems that baffle us, the root cause of the problem was somewhere other than where I was focussing.