You can always add a middleware which adds it to the body from header before coercion

Thank you @UK0810AQ2..I'm new to malli & reitit, can you please give me a reference or sample on middleware

You're using malli in http, are you using it with reitit?

I use malli for schema validation and reitit.swagger for API definition and routes.

How does your ring handler look like?

["/dosomething"
    {:swagger {:tags ["do something"]}
     :post    {:summary    "route the call after validating the payload based on foo or bar"
               :scope      [:api:write]
               :parameters {:header [:map
                                     [:authorization schema/authorization]
                                     [:type schema/type-header]]          ;; foo or bar
                            :body [:map
                                   [:events schema/general-body]]}        ;; this is the part we need to call schema/foo or schema/bar based on type
               :handler    (h/process-api config)}}]

the part events is a generic such that based on the type, we will apply one schema vs the other

That's not the ring handler, just reitit routes

oops.. sorry

(defn process-api [config]
  (fn [{{:keys [header body]} :parameters}]
    (let [events (body :events)
          total  (count events)]
      (let [results    (k/send-events config events header)
            successful (count (remove :error results))]
        {:status (cond
                   (zero? successful) 400
                   (= total successful) 200
                   :else 206)
         :body   {:events results}}))))

You should share your entire code, what about reitit.ring/ring-handler

@UK0810AQ2, Thank you for your advice.. I resolved it.. this is what I did..

(defn process-api [config]
  (fn [{{:keys [header body]} :parameters}]
    (if-let [errors (m/explain i/custom-schema body)] ;; the additional validations
	   {:error 400
	    :body (-> errors m/humanize...)}
	   (let [events (body :events)
	         total  (count events)]
	      (let [results    (k/send-events config events header)
	            successful (count (remove :error results))]
	        {:status (cond
	                   (zero? successful) 400
	                   (= total successful) 200
	                   :else 206)
	         :body   {:events results}}))))) 

This is the very much not what I suggested You should build a full reitit ring handler like in the examples in the reitit repo, then add a middleware to add the parameter from the header to the body

oops!!