Blank checkout page. In-app purchase issue?

I am developing iOS app with Ionic 3. My Android version has built and released successfully. The problem comes to iOS version.

The app is mobile version of my web main platfrom built with Wordpress + Woocommerce. User can checkout the order from app and pay with bank transfer (BACS on Woocommerce). No instant payment using credit card, google play, or app store payment. That’s why my Android app not using in-app purchase plugin. I am using the same method to iOS app.

Everything runs well on iOS app development with Ionic Serve. Checkout page and flow runs perfect. But when it comes to iOS simulator, checkout page shows blank. I have no idea what wrong it is.

I read some documentations and probably my iOS app needs in-app purchase plugin and configuration. But, my app not providing instant purchase. And everthing runs well on Android/Google Play.

Please enlight. Thanks