Update Cost Rate Session Fee
----------------------------

Update the **session fee configuration** for a cost rate.

If ``rate_cost_schedule_id`` is provided, the session fee is applied to the
specified schedule configuration. Otherwise the session fee is applied
to the base cost rate.

The schedule identifier can be either the internal numeric ID or the
schedule UUID.

**Request**

- Method: ``PUT``
- Path: ``/api/dynamic_pricing/cost_rate_session_fee``

**Body parameters**

Mandatory:

.. list-table::
   :widths: 25 15 60
   :header-rows: 1

   * - Name
     - Type
     - Description
   * - uuid
     - string
     - UUID of the cost rate.
   * - amount
     - float
     - Session fee amount.

Optional:

.. list-table::
   :widths: 25 15 60
   :header-rows: 1

   * - Name
     - Type
     - Description
   * - grace_period
     - integer|null
     - Grace period in seconds before the session fee is applied.
   * - energy_threshold
     - integer|null
     - Minimum consumed energy in Wh before the session fee is applied.
   * - rate_cost_schedule_id
     - string|integer|null
     - Optional identifier of the schedule configuration. Can be a
       numeric internal ID or UUID.

**Example request**

.. code-block:: bash

    curl --location --request PUT \
    'https://example.beenergised.cloud/api/dynamic_pricing/cost_rate_session_fee' \
    --header 'x-api-token: <your_token>' \
    --header 'Content-Type: application/json' \
    --data '{
      "uuid": "<COST_RATE_UUID>",
      "amount": 1.3,
      "grace_period": 50,
      "energy_threshold": 600,
      "rate_cost_schedule_id": "<SCHEDULE_UUID>"
    }'

**Response (200)**

.. code-block:: json

    {
      "status": "ok",
      "message": "Session fee configuration was successfully saved"
    }

**Error responses**

- ``404``: Cost rate not found.

.. code-block:: json

    {
      "status": "error",
      "message": "Cost rate not found"
    }

- ``400``: Validation error.

.. code-block:: json

    {
      "status": "error",
      "message": "Session fee exceeds automatic stop"
    }

- ``500``: Generic server error.

.. code-block:: json

    {
      "status": "error",
      "message": "Internal Server Error"
    }