FileTransfer is not defined

I found a solution.

As others have mentioned, and after making sure the File and FileTransfer plugins were properly installed, I removed my android platform, re-added it, built it, and then tested on the device with success.

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These were my steps (From the command line):

ionic platform remove android
(made sure the "adroid" folder in the "platforms" folder was now gone)
ionic platform add android
ionic build android
ionic run (assuming you have a device plugged in to your pc so "ionic run" will load the app on your device)

Hope this can help someone.