If for any reason the Garadget configuration via WiFi is not working, there is a (somewhat geeky) way to configure the unit via USB interface:
Setup Instructions More Setup and Functions Reference Functions Reference
[UPDATE] Particle has released the version of command line interface with the installer for Windows, Mac & Linux, so the process is less geeky now.
I had to resort to configuring one of my units via USB, and was successful doing so. Following the setup instructions, I installed Node.js and particle cli. I connected the device to my computer’s USB port. Then the following commands: