Greetings from Com2uS!
Currently, there's an error where users are unable to connect to the game when they select a server without a name at Option > Select Server on iOS devices after the Mar. 23rd Update.
Please note that this error will be resolved with the next update, and try quitting and restarting the game to resolve the error for those who're experiencing this issue.
We apologize for any inconveniences this may have caused and thank you for your understanding!