First of all, please make sure that the latest version of the game is installed on your device.
Using an old version of the App might cause purchase issues.

In order to access the Dragon City Shop you first need to open the App, then follow these steps:

1. Click on the “Shop” button (bottom right corner).
2. Click on the "Packs" section.
3. Select the amount of gems you wish to purchase and follow the payment process.

If by any chance you don't receive your purchase, please check "Where is the purchase I made?" in the FAQ.