curl --request PATCH \
  --url https://api.scalev.com/v3/stores/{store_id}/public/cart/items/{item_id} \
  --header 'Content-Type: application/json' \
  --header 'X-Scalev-Storefront-Api-Key: <x-scalev-storefront-api-key>' \
  --data '{
  "quantity": 2
}'

{
  "id": 123,
  "item_count": 123,
  "total": "<string>",
  "items": [
    {
      "id": 123,
      "type": "variant",
      "variant_id": 123,
      "bundle_price_option_id": 123,
      "quantity": 2
    }
  ]
}