Gating services on unpaid balances

The strongest pattern this API enables: let your own system cut off service when your customer owes you money — and restore it when they pay.

GET /v1/customers/{id}/balance        (customers:read — cheap, poll freely)
GET /v1/customers?pastDue=true        (nightly reconcile list)

The balance is always computed (gross + reminder fees − paid − credited across all open invoices) — never a stale status field:

{ "outstandingOere": 125000, "overdueOere": 125000, "overdueCount": 1,
  "oldestDueDate": "2026-07-17", "daysOverdue": 10, "collectionsOere": 0,
  "pastDue": true }

pastDue is threshold-evaluated: configure “notify me above X kr / Y days overdue” so a single small invoice doesn’t flip the flag. Webhooks customer.past_due and customer.settled fire on the transition only (never repeated daily) with the customer id and sequence number in the envelope’s customer block.

Push is the signal, pull is the truth: webhooks can be lost or arrive out of order — gate on the balance endpoint, use the events to know when to check. A customer who blocks access on a lost event blocks forever.