curl --request GET \
  --url https://api.helloproper.com/pending-bills \
  --header 'Authorization: <api-key>'

{
  "bills": [
    {
      "dueDate": "<string>",
      "pendingBillLineItems": [
        {
          "productKey": "<string>",
          "amount": {
            "currency": "<string>",
            "amount": 123
          },
          "quantity": 123,
          "unitNetPrice": {
            "currency": "<string>",
            "amount": 123
          },
          "netPrice": {
            "currency": "<string>",
            "amount": 123
          },
          "vat": {
            "taxMode": "<string>",
            "taxRate": 123
          },
          "accountingPeriod": "<string>"
        }
      ],
      "subtotal": {
        "currency": "<string>",
        "amount": 123
      },
      "total": {
        "currency": "<string>",
        "amount": 123
      },
      "vatTotals": [
        {
          "vat": {
            "taxMode": "<string>",
            "taxRate": 123
          },
          "amount": {
            "currency": "<string>",
            "amount": 123
          }
        }
      ]
    }
  ]
}