If the app closes every time you try to open it, this is either an issue with memory on your device or an issue with your device's OS version, as we don't often hear of crashes with MileIQ.
First, verify that the version of iOS on your device is iOS 8 or above, as we no longer support iOS 7 or below. The iOS on your device can be updated by opening the Settings app on your device > General > Software Update > Download and Install.
Alternatively, unexpected app closures can be caused by memory issues on the device. Please try quitting some of the apps currently running in the background by double-clicking the center "Home" button on the iOS device and then swipe any unused applications up and off the screen (except MileIQ, of course!). This technique often frees up memory on your device and is recommended from time to time, especially on older devices.
See here for more information about force-quitting applications on iOS.
Alternatively, the device may be close to its storage capacity. Applications need some available storage space to be able to open and freeing up some storage may help. Please try deleting some unused items from the device.
See here for more information about managing storage on iOS.
Verify that the version of Android on your device is 4.4 or greater (Kit Kat, Lollipop, or Marshmallow). Depending on your device and the version of Android, find the device settings.
The easiest way to do this is to view all installed apps on your device and select the 'Settings' icon. Then, find the 'About Device' or 'About Phone' in the list of options and tap on 'Software update' to see if a new version of your OS is available. If there is, tapping 'Install Now' will download the new OS version.
Staying on the most current version of the Android OS will ensure that MileIQ runs optimally.