Retrieve a specific invoice for the authenticated client.

Poll this endpoint while a payment clears. Payment is complete only when the status is Paid. A Payment Pending invoice (an in-progress ACH or SEPA direct debit, for example) has not completed.

To hand the shopper off to a WHMCS payment page, use the POST /user/invoices/{invoice_id}/payment-link endpoint.

{
  "data": {
    "id": 456,
    "invoice_number": "0001",
    "date_created": "2026-07-01",
    "date_due": "2026-07-15",
    "status": "Unpaid",
    "subtotal": 10,
    "total": 10,
    "balance": 10,
    "payment_method": "stripe_dynamic"
  }
}