Create Cost Rate Energy Cost
----------------------------

Create a new **energy cost interval** for a cost rate.

If the cost rate uses dynamic pricing schedules, the energy cost can be
associated with a specific schedule by providing ``cost_rate_schedule_uuid``.

**Request**

- Method: ``POST``
- Path: ``/api/dynamic_pricing/cost_rate_energy_cost``

**Body parameters**

Mandatory:

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

   * - Name
     - Type
     - Description
   * - cost_rate_uuid
     - string
     - UUID of the cost rate.
   * - unit
     - integer
     - Energy unit in Wh (e.g. 1 = per Wh).
   * - price
     - string|float
     - Price per unit.

Optional:

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   :widths: 25 15 60
   :header-rows: 1

   * - Name
     - Type
     - Description
   * - cost_rate_schedule_uuid
     - string|null
     - UUID of the schedule configuration (recurring or unique pricing config).

**Example request**

.. code-block:: bash

    curl --location --request POST \
    'https://example.beenergised.cloud/api/dynamic_pricing/cost_rate_energy_cost' \
    --header 'x-api-token: <your_token>' \
    --header 'Content-Type: application/json' \
    --data '{
      "cost_rate_uuid": "<COST_RATE_UUID>",
      "unit": 1,
      "price": "0.25"
    }'

**Response (200)**

.. code-block:: json

    {
      "status": "ok",
      "message": "Energy cost was successfully created.",
      "uuid": "29ccce27-3a3a-4308-831a-ed68b460e3bf"
    }

**Error responses**

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

.. code-block:: json

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

- ``404``: Schedule not found.

.. code-block:: json

    {
      "status": "error",
      "message": "Schedule not found"
    }

- ``400``: Duplicate energy cost interval (same unit already exists).

.. code-block:: json

    {
      "status": "error",
      "message": "Energy cost interval already exists"
    }

- ``500``: Generic server error.

.. code-block:: json

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