Hiya,
Thanks Brad. Yep, it's true: you actually need the adaptor/cable combo. It took me about 4-5 USB-A to USB-micro cables, but FINALLY found one that worked.
I'm afraid i don't know what makes that one special, but at least the app and the synth recognize each other now. I really hope there's a firmware fix for this soon because it really shouldn't be this hard, but at least I got there.
And for anyone having a similar issue, do NOT get the IK Multimedia cable! Although the advice was offered elsewhere on the forum with good intentions, buying that cable does NOT guarantee you a connection.