Hi @Vimutisuk!

Piggy Bank is a purchasable feature so in order to collect the Gold Bars, you need to purchase it for the price that is stated when you tap on it.

Buying a Piggy Bank isn't crucial in your gameplay, but does offer a lower priced way to add Gold Bars to your game than buying in the Store bundles.

Gold Bars are also sometimes available in small amounts as rewards for various events and challenges in our games, so keep checking for other ways to add to your collection!

Hope this clears out any doubts 😊