Disregard URI answer, he doesn't know anything.
The problem is simple, Whilst your bike was not operating for 3 months there has been no activity for the fuel... so, the fuel grows something like a moss or fungi in the tank... this is in the form of clogs, which is usually white for unleaded fuels.
So to make the engine to turnover again to start. All you need to do is, empty the fuel from the tank (Professionally or DIY) and fill it back up again with NEW FUEL.
Or keep trying to start the engine with electric start to eventually hit good passing fuel through to the engine which will start it up... Though keep the engine on idel for at least 5 - 10 minutes to clear out any leftover white clogs.
So when you leave your bike for an extended period of time (over 5 days) get someone you trust to turn on engine every 2nd day to clear out any white clogs, for only about 2 minutes.
And turn OFF the fuel switcher to prevent any fuel flow to the engine, which creates the white clogs.
Hope this helps and if you do one of the suggested things above and turn off the fuel flow when you leave the bike you will be a happy chappy
Motorbike owner and pretty damn good DIY mechanic