You don't even need to enter in-game, if that "TERA Club account" appears on the right side at the top, then gtg. For test only load server till arbiter server, that's enough for reach character screen.
For some reason when a use the net core api my launcher doesn't work. ill' check if there's something wrong with my LauncherloginForm
Update.
Tried several times with net core api but the launcher got several errors
From LauncherloginForm
Alert --------------------Result
alert('responseText:'+jqXHR.responseText);-----> Empty
alert('url:'+jqXHR.url); ------> Undefined
alert('status:'+jqXHR.status); -----> 500
alert('readyState:'+jqXHR.readyState); ------> 4
alert('statusText:'+jqXHR.statusText); ------> Internal Server Error
But if use the grails or tomcat API, this does not occurs