You need to copy the lotatc.key file that you must received after buying LotAtc in your user folder: C:\Users{Me}\LotAtc 4 DCS Data\Client or launch LotAtc client, it will display you the right directory, just click on it to open the folder. If you didn’t buy a licence, you may use LotAtc 4 DCS in unregistered ‘demo mode’, with limitations described here.