const { result, error } = await unprice.invoices.get({
  invoiceId: "inv_1234567890"
});

if (error) {
  console.error(error.message);
  return;
}

console.log(result);

{
  "invoice": {
    "id": "inv_1234567890",
    "status": "paid",
    "currency": "USD",
    "gross_amount": 100000000,
    "amount_due": 0,
    "amount_paid": 100000000,
    "amount_included": 0
  },
  "lines": []
}