Your account will be locked if you enter the wrong password for a specific number of times when you log in to your Yu ID.
This account lock will be automatically removed after a certain time. Try to log in again after it is removed.
Note that if you are in a hurry or if you have forgotten your password, you can readily remove the account lock and use the account, by resetting the password.
To reset password
https://mypage.jpid.pf.japanpost.jp/password/reset/request
(Image of the Yu ID login screen when the account is locked)