There was a functional product in beta (as in: being used by non-employees) in early 2012. The issue was that Lucas was unable to secure appropriate relationships with banking partners such that the product could actually launch to the mass public until the end of 2014. Both attempted banking partners had extreme restrictions on the number of users allowed on the system until their legal teams signed off on it (due to the timely influx of new regulations from the CFPB), and both times this took more than 9 months to go through their bureaucracy.
Even while these public-launch-restrictions were in place, obviously it was possible to demo investors on the real product that moved real money between real bank accounts using real ultrasound technology to buy from real merchants, etc. These features were all also in beta tester hands.
As far as why investors were willing to invest in the product.. that's its own discussion that I don't feel like typing up at 6:30 on a Friday. Short answer: mobile payments were hot, the product really was pretty and functional, the go-to-market strategy (assuming a banking license deal went through) was rather pragmatic (debit cards to be backwards compatible & get data from day one), the team (other than the CEO) top-tier, no investor invested particularly much, etc.