According to a support forum post, the latest update to the Pebble app for iOS contains a critical issue that prevents the application from working. The company is working on a fix, but, in the meantime, it is asking users to delay installing the version 2.1 update that was released today, Monday, March 31st.
The app is temporarily hidden from the iTunes App Store while Pebble tries to resolve the issue. iOS owners with automatic updates enabled should turn off the feature by going to Settings > iTunes & App Store and toggling Updates OFF in the "Automatic Downloads" section.
If you already have version 2.1 installed, there may be a temporary work around that allows you to install the previous version 2.0.2.
Update: We received the following statement from Pebble:
"Today we experienced an issue deploying version 2.1 of the Pebble iOS smartphone app. We've pulled the update from the App Store for now. We're working with Apple to fix this problem as quickly as possible, and will notify customers when an update is available that resolves the issue. We sincerely apologize for any inconvenience. Please check our forums for more information."