> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ageneral.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Usage and billing

> Credits, virtual keys, agents, and billing errors

## Overview

Usage through **`https://models.ageneral.ai`** draws **Ageneral account credits** from the **project owner** wallet when billing gates apply. Checks run **before** upstream inference on gated routes.

## Credits

Credits raise the balance available for **Models** usage. When the balance is exhausted, gated routes may return **402 Payment Required** until credits are added.

## Virtual keys

**Virtual keys** use the **`sk-bf-…`** prefix. Scope them to your account or **project**; spend rolls up to the **project owner** wallet. Use them for scripts, tools, and extensions that call **`models.ageneral.ai`** directly.

## Billing for agents

Inference initiated by **Ageneral-hosted agents** uses **project-scoped** access and consumes the **same balances** and gates as **virtual-key** traffic initiated by your applications.

Application code should continue to use **virtual keys** when **you** call **Models**.

## Error reference

| HTTP    | Meaning                                                              |
| ------- | -------------------------------------------------------------------- |
| **401** | Missing or invalid **`Authorization`**, or unsupported API key shape |
| **402** | Insufficient credits                                                 |
| **503** | Billing or inference unavailable                                     |

## Next steps

* [Authentication](/authentication)
* [Agents](/agents)
* **API reference** → **Models**