Your device desperately needs updating its device OS - 0.5.4 is aaaaanciean.
Due to that outdated device OS you are running into an issue that’s also in connection with not fully applying the documentation’s instructions/warnings
Particle.variable() syntax is also outdated. It should be
You also don’t show what the reported error was - I guess that would have give a clue in that direction too.
In your screenshot you should also reveal the settings hidden behind the
> button next to your device name
There you can also check whether the device is online/reachable by hitting the SIGNAL button (or the icon next to the device name in the status bar)
The empty/black circle between device name and device OS version also suggests your device is not online.