You are downloading the Pebble Notifications APPX file v2015.325.2322.1471 for Windows Phone. Pebble Notifications is a free and useful Productivity app: Pebble application for Windows Phone. This is an internal test application to get feedback on Accessory Ecosystem Support feature in WP Blue GDR1. ... You can now download the offline APPX file to install & try it.
Download Locations for Pebble Notifications 2015.325.2322.1471 APPX file
Important Notice: Now Due To Unspecified Limitations, You Can Not Use The Offline APPX File To Install It Any More.
To try to install it manually from an SD card, you should choose one of the server location above to get the offline Pebble Notifications APPX file, move the file to your phone's SD card and then tap 'Install local apps' in the phone's App list.