Konami responded to my mail:
Basically, the MGO Store (PlaystationStore version) is not up yet.
About PlayStationrNetwork Wallet Payments:
The PlayStationrNetwork Wallet payment option will not be available at launch on March 17 for Expansion Pack ver.1.30.
Updates regarding this issue will be provided as soon as more information becomes available.
After downloading Expansion Pack 1.30, the “MGO Shop (PlayStationrNetwork)” option will appear in the START MENU.
However, please be advised that until PlayStationrNetwork Wallet payments are enabled, an error message will be displayed when this menu item is selected.”
At this time we are not currently accepting the PlayStation Network Wallet payment method.
Regards,
KDE-US Support
kdeussupport@konami.com
Basically, the MGO Store (PlaystationStore version) is not up yet.