# How-to Guides

## Add Products and Services (Inventory)

Once you have a customer, the next step is to add the products and services sold to this customer as inventory items.

**Usage Product Inventories:**

Use `POST /usage-product-inventories` to create usage-based products (e.g., call charges, data usage).

**Rental Product Inventories:**

Use `POST /rental-product-inventories` to create fixed rental products (e.g., monthly line rental, broadband packages).

**Example - Creating a Usage Product Inventory:**


```json
{
  "customerId": 123,
  "siteId": 456,
  "usageProductId": 789,
  "usageProductReferences": [
    {
      "reference": "01234567890",
      "primary": true
    }
  ]
}
```