you can't add an existing invoice.

src/cljs/auto_ap/views/pages/unpaid_invoices.cljs

@@ -259,7 +259,8 @@
                                                                       :location
                                                                       [:expense_account [:id :name [:parent [:id :name]]]]]]
                                                   ]]}]}  
-       :on-success [::invoice-created]}})))
+       :on-success [::invoice-created]
+       :on-error [::invoice-create-failed]}})))
 
 (re-frame/reg-event-fx
  ::edit-invoice-save
@@ -331,6 +332,11 @@
                                 invoices)))
               (dissoc ::handwrite-checks))})))
 
+(re-frame/reg-event-fx
+ ::invoice-create-failed
+ (fn [{:keys [db]} [_ data]]
+   {:dispatch [::events/modal-failed ::new-invoice "That invoice already exists."]}))
+
 (re-frame/reg-event-fx
  ::invoice-created
  (fn [{:keys [db]} [_ {:keys [add-invoice]}]]