I bought sylenth for my new Mac Book Pro but once i installed it i tried to regrester it in ableton copied the lisenese file to the sylenth programme file and restarted Ableton it was still in demo mode.
Just make sure the .DAT is in the right folder…
You know the way with Macs… You’ve got the system folders… and the “Your Name” folders?
I cant remember which one it goes into - but maybe try sticking it in the other to see if it makes any difference.