Update leverage for an instrument.

Each setting resolves independently: explicit per-instrument setting, then exchange-managed account-group default, then instrument maximum leverage and isolated margin. Group leverage is capped at the instrument maximum; a group cross default resolves to isolated on isolated-only instruments. Group defaults apply to new listings and never overwrite explicit settings. This operation sets both settings explicitly; GET /v1/account/config reports resolved values. Submit the current resolved pair to preserve it against later group changes. Leverage bounds and BLP locks also apply to unchanged values. Set your preferred leverage and margin mode after listing and before placing your first order. An unknown instrument ID (never listed) is rejected with instrument_not_found; a disabled instrument is not rejected merely because it is disabled.

Margin mode can change only when the account has no position and no open orders in that instrument, including orders awaiting risk approval or execution. Close the position and cancel all orders before switching between isolated and cross margin. A position blocks a mode change with position_exists; open orders block it with open_orders_exist. Leverage changes within the same mode remain subject to leverage limits and margin checks. Leverage must be positive (lev: 0 returns 400); exceeding the instrument maximum returns invalid_leverage. BLP-subscribed instruments reject leverage or mode updates with blp_leverage_locked; unsubscribe before changing the configuration.

Requires proxy signature, see proxy signing.

{
  "op": {
    "args": {
      "iid": 1,
      "lev": 10
    }
  },
  "sig": "0x1234567890...",
  "salt": 1234567890,
  "ts": 1767225600000
}

{
  "instrument_id": 1,
  "leverage": 10
}