When you buy a new one it comes locked. You then have to email Henk and he'll send you an unlock code for the first car, as well as the 98 ron calibration, for free. After that, you have to pay.
I'm guessing that as you aren't the person who bought the RSTuner, Henk won't do it for you for free.
Having looked into the pricing, it's mind boggling that people still buy them second hand. It's cheaper to just buy a new one for 180 quid than it is to buy secondhand for ~£120, then pay another 90 odd quid for the unlock and map.