Hello. This is the Gravity Co., Ltd. Ragnarok Zero Operations Team.
We have confirmed an issue where the 
Essential Package (7 Day) item cannot be purchased from the in-game CASH SHOP after the regular maintenance on October 20th (Wed), and the responsible department is currently investigating the matter.
For customers who wish to purchase the Essential Package (7 Day) item, we apologize for the inconvenience, but until the issue is resolved, please purchase it through the RO SHOP on the official website instead of the in-game CASH SHOP. We will work to fix this issue as soon as possible.
We apologize for the inconvenience caused to your gameplay, and we will strive to provide a more stable service environment.
Thank You.
Gravity Co., Ltd. Ragnarok Zero Operations Team