Fix the regression introduced in #8580

cmd/admin-handlers-config-kv.go

@@ -130,6 +130,11 @@ func (a adminAPIHandlers) SetConfigKVHandler(w http.ResponseWriter, r *http.Requ
 		return
 	}
 
+	if _, err = cfg.ReadFrom(bytes.NewReader(kvBytes)); err != nil {
+		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
+		return
+	}
+
 	if err = validateConfig(cfg); err != nil {
 		writeCustomErrorResponseJSON(ctx, w, errorCodes.ToAPIErr(ErrAdminConfigBadJSON), err.Error(), r.URL)
 		return