Jeskola, you may wish to also check the notes here:

http://www.tela.gov.hk/english/doc/w.../lottery_e.pdf

In particular there is a ban on cash prizes and on private gain for individuals connected with the lottery.

For "trade promotions" there more relevant guide is here

http://www.tela.gov.hk/english/doc/licence/TPCLGA.pdf

Here you can't charge a fee for entry and again can't offer a money prize.