There are two types of paid products, and both have different purchasing methods.
Before we explain how to purchase, please make sure to enable Steam Overlay in order to purchase paid items.
1. How to purchase NP
You can purchase the desired quantity of NP from [In-Game Store] - [NP].
2. How to purchase DLCs
[STEAM] - [Eternal Return] - [Store] - [Content for this game].
DLCs must be claimed from your in-game library after purchase.