curl --request GET \
  --url https://api.thundercompute.com:8443/v1/invoices/upcoming \
  --header 'Authorization: <api-key>'

{
  "card_on_file": true,
  "current_credit": 123,
  "last_update": 123,
  "latest_period_end": 123,
  "latest_period_start": 123,
  "total_amount_due": 123,
  "upcoming_invoice": {
    "currency": "<string>",
    "due_date": 123,
    "lines": [
      {
        "amount": 123,
        "currency": "<string>",
        "description": "<string>",
        "id": "<string>",
        "period_end": 123,
        "period_start": 123,
        "price_id": "<string>",
        "quantity": 123
      }
    ],
    "period_end": 123,
    "period_start": 123,
    "subtotal": 123,
    "total": 123
  }
}