Update quote item quantity for one or more quote items.
Sample Curl
curl --location --request PUT 'https://mygatewayurl.com/V1/storeview/default/user/quote/item/17' --header 'Authorization: Bearer qsk2p2azmuylkcgsuhhkbale7vk571vn' --header 'Content-Type: application/json' --data '{ "cartItem": { "item_id": 17, "sku": "Product with tier price", "qty": 100, "name": "Product with tier price", "price": 90, "product_type": "simple", "quote_id": "54" }}'

Sample Curl configurable products
curl --location --request PUT 'https://mygatewayurl.com/V1/storeview/default/user/quote/item/187' --header 'Authorization: Bearer qsk2p2azmuylkcgsuhhkbale7vk571vn' --header 'Content-Type: application/json' --data '{ "cartItem": { "sku": "4-1157", "qty": 3, "quote_id": "219", "product_option": { "note": "Use product option only when updating configurable product child", "extension_attributes": { "configurable_item_options": [ { "option_id": "93", "option_value": 58 }, { "option_id": "141", "option_value": 168 } ] } } }}'