Create product variant

curl --request POST \
  --url https://api.shoppex.io/dev/v1/products/{id}/variants \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "title": "New",
  "description": null,
  "price": 9,
  "price_modifier": null,
  "stock": 3,
  "stock_delimiter": null,
  "license_period": null,
  "file_id": "550e8400-e29b-41d4-a716-446655440000",
  "dynamic_webhook": "https://example.com/variant-hook",
  "option_values": {
    "region": "eu"
  },
  "is_default": false,
  "sort_order": 0
}
'

{
  "data": {}
}