1.Open console with ~
2. Enter ' promo 1kuz4kwk '

IF IT DOESN' WORK:
A simple trick I have tried was to go to Settings of STEAM, change the download region to one of the EU countries and it should then work for you.
AND
Check that your keyboard is using the QWERTY format too else you can't boot up the console of game.
AND
Also make sure you enter in the GRID screen where you can select guns!

Cheers!