Using Capacitor Plugins In Iframe (parent is Ionic)

My App is configured as Ionic 3 + Cordova + Capacitor(Forced Integrated).
works good itself.

the point is, i want to integrate other webapp using Capacitor Plugin at Ionic 3 using Iframe.
however, it doesn’t work.

the app in the iframe cannot recognize Capacitor Plugins. how should i solve it?