3D FlipBook - Fontawesome Icon not visible in iOS app

Hi, they display well in the PC's web browser and iPhone's Safari browser. However, they don't display in the app's in-browser. The icons in the bottom menu bar and the icons for the page turning button in the center of the screen are not displayed.

I copied the necessary files to 3d-flip-book in the root path. https://my-domain/3d-flip-book/

The settings were as follows. (This is only visible when I edit this text)

I am using the paid version. Do you have any advice for me? Maybe there is a path problem. If there is another way to specify the path to each file, please do so as well.

Thanks,