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There are 2 reasons for that. Both you can catch when using the Green button ↓ during the app creation process:

1. Your web site does not show at all

This happens both, when you press the Green button ↑, or when you access the app from an icon. 

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When you want to limit frame usage only to the Mobsted app engine - open permission for  *.mobsted.com 

2. Your web site does not scale to mobile screen width

This happens both, when you press the Green button ↑, or when you access the app from an icon. 

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