Pfthb

I'm taking luminus for a spin. It is confusing. How do I manage to give a json formatted response? My understanding from the docs is that if I set the content-type as json, then the wrap-format middleware should see that and know how to serialize the data. However when I set the content-type I get "java.lang.IllegalStateException: Can't coerce body of type class clojure.lang.PersistentArrayMap"

After trying lots of things this is what I understand should work:

(defroutes home-routes
 (GET "/" 
 (home-page))
 (GET "/docs" 
 (-> (response/ok (-> "docs/docs.md" io/resource slurp))
 (response/header "Content-Type" "text/plain; charset=utf-8")))
 (POST "/upload" [file]
 (->(response/ok (assoc :inserted (->> (upload-file resource-path file)
 load-sheet
 persist-sheet
 count-ones
 )
 )

 )
 (response/header "Content-Type" "application/json")
 )
 ) 
 )

This is my current setup of wrap-formats:

(defn wrap-formats [handler]
 (let [wrapped (-> handler wrap-params (wrap-format formats/instance))]
 (fn [request]
 ;; disable wrap-formats for websockets
 ;; since they're not compatible with this middleware
 ((if (:websocket? request) handler wrapped) request))))

and this is formats/instance:

(def instance
 (m/create
 (-> m/default-options
 (assoc-in
 [:formats "application/json" :opts :modules]
 [(JodaModule.)])
 (assoc-in
 [:formats "application/transit+json" :encode-opts]
 :handlers org.joda.time.DateTime joda-time-writer))))

What am I failing to see?
Thanks in advance.