curl --request GET \
  --url https://api.withflex.com/v1/checkout/sessions/{id}/line_items \
  --header 'Authorization: Bearer <token>'

{
  "line_items": [
    {
      "line_item_id": "obj_01EXAMPLE00000000000000000",
      "amount_discount": 0,
      "amount_subtotal": 0,
      "amount_tax": 0,
      "amount_total": 0,
      "amount_shipping": 0,
      "amount_fee": 0,
      "description": "string",
      "fees": [],
      "price": {},
      "quantity": 0,
      "eligibility": "not_eligible",
      "shipping_rate": "string"
    }
  ]
}