To get lucky stamps for free coins, you needed to purchase coin packages from the shop, each package has a stamp. Please check the screenshot for reference.

One stamp will be awarded to you for each in-app purchase you make. If you gather four stamps, you will be qualified for additional bonuses and free coins.

-In a coin shop, you can find out the status of your stamp.

To check your status for the Lucky Stamp: please refer to the screenshots provided below:

First, locate the shop in the upper middle part of the main lobby of the game.

Second, it will direct you to the shop and you can find the Lucky Stamp below.

When you purchase a product, you will get a stamp.

If you fill up all the stamps, you can get a reward.

Take Note: Be aware that stamps are only given as part of coin purchases.

Therefore, booster products are exempt from the requirement.

Please check the screenshot for reference that boosters don’t offer stamps.