I'm not sure how good an idea it is to ask the participants to share the order ID, it sounds quite deanonymizing. I understand that the purpose of the promotion is to attract new users, but perhaps we should look for a different way.
I just realized asking for TX ID
might make the transaction page public to everyone. From next rounds we will consider asking it only from the winner. In this round I can not see anyone provided the ID yet but if anyone doesn't want to publish it and wants to keep it secret then they can but if they win and take more than one slots to receive the reward, they will need to provide the ID in private. The ID will be sent to the management for verification before sending the reward.