curl --request POST \
  --url {protocol}://{host}/wp-json/cocart/v1/item \
  --header 'Content-Type: application/json' \
  --data '{
  "cart_item_key": "<string>",
  "quantity": "<string>",
  "return_cart": false
}'

{
  "key": "<string>",
  "product_id": 123,
  "variation_id": 123,
  "variation": {},
  "quantity": 123,
  "data_hash": "<string>",
  "line_tax_data": {
    "subtotal": [
      123
    ],
    "total": [
      123
    ]
  },
  "line_subtotal": 123,
  "line_subtotal_tax": 123,
  "line_total": 123,
  "line_tax": 123,
  "product_name": "<string>",
  "product_title": "<string>",
  "product_price": "<string>",
  "product_image": "<string>"
}