It shows error message ”User authentication failed.“, what should I do?

How to Play & Controls

To maintain the integrity of the application, the device authentication feature provided by the platform (Apple or Google Play) has been implemented as a security measure in this game.

The displayed error message, "User authentication failed", is not a bug but is related to your current usage environment.
We recommend trying the following steps to resolve the issue.

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▼① Caused by Communication Environment
There is a possibility that the temporary access issue is being caused by the internet environment.

・Please wait a while and try logging into the game again.

▼② Caused by the Device in Use
If the above step ① does not resolve the issue, it is possible that the device in use is not supported to run this app. In this case, you may not be able to continue playing on your current device. We recommend transferring your game data to another device and checking if the game functions normally.

・ Prepare another smartphone or tablet
・Transfer your game account data
※To transfer your game data, please make sure to link your game account to an external service account in advance.
For details, please refer to the FAQ on "Data Transfer" below.

▼How can I transfer my game data to another device?
Apple: Check Here
Google Play: Check Here
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■ Important Notes
・The target device for data transfer must be an official Android or iOS device, and their OS meets the requirements for running this app.
・When transferring data between different operating systems (Android ↔ iOS), Dragon Stones will not be transferred.
・Devices other than smartphones or tablets are not supported.
・We are unable to provide individual responses or instructions regarding the details of devices that are not supported.