Same here, purchased after originally trialling on Windows which expired, then installed trial on Linux Mint, logging in with same account and purchasing, the Expired Trial message does not go away or let me sync.
I strongly suspect the company is taking our money but manually authorising accounts for some bizarre reason, and being the weekend, we aren't getting any action. Poor show Insync!
edit: in fact, it seems I am correct, see the following links. No automated account set up Insync? Think its time to move into the modern world of business!!
What really irks me about this, is that there is no clear indication of this process (there are a couple of well hidden pages, one example here and no email messages either) and I've bought this on a Sunday when I have time to play with the app and get it up and running on my systems. Now I have to wait for Insync staff to turn up on Monday morning, and I won't have time to get working on this again until next weekend. So Insync have my money, I have paid for something I cannot use for another week.