If the internet connection makes your app screen blank, you will see an error log at the same time saying invalid key. Please make sure the license key you are using is valid and bundle id is paired.
If you still cannot find out the problem, please send us your account name and the license key you are using through email. We can only make sure the license key is valid with its website value, so please make sure the license and the bundle id are all correct at your app side.