We're aware that some iOS users are experiencing issues accessing the game. To resolve this issue, please try offloading the app or deleting it and then installing the game again.
To offload the game, go to Device Settings -> General -> iPhone Storage, and then wait for it to load. In the list of apps, click on Bullet Echo then press "Offload app" and confirm.
Meanwhile, we're investigating the issue itself to provide a quick fix.