First of all, you are not able to run the game during the server maintenance.
Please visit the official website/community to check whether the maintenance is ongoing.
If you can’t run the game even when the server is not under maintenance, please follow the steps below to troubleshoot;
[How to solve the issue]
1. Delete unnecessary applications or data.
2. Check your OS version and update it to the latest version.
3. Check your network connection status (Wi-Fi or mobile data).
4. Reboot your mobile device.
※ If you are unable to run the game continuously, completely delete Dark and Darker Mobile, and reinstall it after ensuring you are connected to a stable network (Wi-Fi or mobile data).