Is scratch card haram when it is given free instead of purchased?

In my scenario, a gas station is giving away scratch cards for filling fuel. If you fill for a certain amount, you get a scratch card for free with a chance to win something. You are not charged for the scratch card. In fact, the gas station themselves is losing money by doing this. They are doing this to attract customers to their station. The prices are car shampoo and cash. From my point of view this seems to be halal. What do you think?