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

# v3 Authentication

> Authenticate an interactive or headless client to the account-resolved v3 MCP endpoint.

Connect to `https://api.interchange.io/mcp/v3` with OAuth or an organisation
API key. The credential determines the home account, reachable accounts, and
permissions; the URL does not select Buyer or Seller behavior.

* Use OAuth for interactive clients and human-authorized work.
* Use an organisation API key for headless automation, stored in a secret
  manager and sent as `Authorization: Bearer YOUR_API_KEY`.
* Grant only the permissions the integration needs. A visible tool may still
  refuse a write when the credential lacks the required permission.

Call `get_status` after authentication. A successful connection proves that
the credential is valid, not that the active account is enrolled in the v3
preview.

<Card title="Full authentication reference" icon="book" href="/v2/authentication">
  Review OAuth, organisation API keys, service tokens, permissions, and stable
  v2 versioning behavior in the canonical authentication guide.
</Card>