> ## Documentation Index > Fetch the complete documentation index at: https://docs.nozle.dev/llms.txt > Use this file to discover all available pages before exploring further. # Product Credits Overview > Customer-level credit systems, balances, sources, and ledger behavior Nozle product credits are product-level units used to authorize metered actions. They are separate from invoice wallet credits, which apply monetary value to invoices. ```text theme={null} feature -> exact conversion rate -> credit system -> customer sources ``` For example, one `agent_execution` event can cost `2` AI credits while one `voice_call_minute` costs `4` AI credits. ## Core objects * **feature:** measures the product action. * **Credit system:** names the shared pool, such as AI Credits. * **Metric rate:** stores the exact metric-to-credit ratio and its effective history. * **Plan grant rule:** defines included credits and cadence. * **Balance source:** keeps each plan grant, paid top-up, or adjustment separate. * **Operation and allocation ledger:** explains every accepted, denied, granted, or adjusted amount. Product credits are not invoice wallet credits. Do not use wallet endpoints or the legacy `/check-and-deduct` adapter for new credit-system integrations. ## Customer and Entity pools Customer balances remain the shared pool. Entities add stable per-user or per-project attribution, per-Entity grants, and optional shared fallback without replacing that pool. A successful usage request atomically deducts the configured source order and writes an immutable operation before its billing event is published through the durable outbox. ## Read access Server code can read balances with a restricted secret key. A publishable key cannot read the ledger or any other customer data. Expose only the required fields through your own authenticated backend endpoint.