How to redeem your Japanese Playstation Prepaid card
Log-in with your Japanese Account.
Go to the PlayStation Store, it will be located as usual on the far left of your screen.
Scroll to the bottom of the sidebar and tap “コード番号の入力” button. The one we circled in red below.
Carefully enter the 12 digits code.
Hit the right button. Your account will now be credited with the amount of the Gift card.