Note, you may need to allow installing apps from unknown sources. To enable this setting, follow these steps:

1. Navigate to Setting > Security.
   
   
2. Check the option Unknown sources.
   
   
3. Tap OK on the prompt message.
   
   
4. Select Trust.

Why isn’t the app in the Google Play store? It seems that Google may view Photo Backup Stick as unwanted competition to their cloud services, therefore, we’re forced to have our users install the app manually, rather than from the app store.