How do boosters work?
You can find a description of all boosters in the Hotel Upgrades catalog under the Power-ups tab.

As you play, you’ll receive booster tokens. You need to collect 30 tokens to get one booster.

What are keys used for?
Keys are used to unlock Premium Hotels.

You can find the available Premium Hotels in the corresponding tab of the hotel selection menu, which you can open by tapping the airplane icon.

What are green banknotes used for?
Green banknotes are used to unlock Unique Hotels.

You can find the available Unique Hotels in the corresponding tab of the hotel selection menu, which you can open by tapping the airplane icon.