curl --request PUT \
  --url 'https://api.stateset.com/api/v1/carts/{id}/items/{item_id}' \
  --header 'Authorization: Bearer YOUR_API_KEY' \
  --header 'Content-Type: application/json' \
  --data '{
  "discount_amount": null,
  "quantity": null,
  "unit_price": null
}'

{
  "discount_amount": "string",
  "id": "string",
  "name": "string",
  "product_id": null,
  "quantity": 1,
  "sku": "string",
  "total": "string",
  "unit_price": "string"
}