Hi joonjung, this is a known issue that is being worked on at the moment.

In the mean time you are able to work around this issue by adjusting the screen.

Please hold down the CTRL button (Command button for MAC) and then press either the + or - button once.

This will adjust the screen as well as unlock the drop down menu so you can select Monthly for your pay schedule. 

Try that out and see how it works.

Kristian.