One-time credential exchange. After signing a partnership agreement,
OpenFiskal emails a setup token (ofk_setup_...) to the POS vendor’s
technical contact. POST it here to receive your first platform API key.
This endpoint is unauthenticated — the setup token is the sole proof
of identity. It can only be used once. After successful exchange, use
the returned API key in the Authorization: Bearer header on all subsequent requests.
If the token has already been consumed or has expired, the endpoint
returns 401.