1. Make sure your date and time is set correctly, especially the year.
  2. Verify that the build you're downloading was built for the correct platform (ie. trying to install an iOS build on an Android phone won't work).
  3. If installing to an iOS device, make sure the build's provisioning is correct for your device ("Unable to Download..." error).
  4. Ensure you have enough free space (common on older Android devices).
  5. Reboot the device.
  6. Try another device.

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- Build Failure