vendure/packages/dev-server/load-testing/graphql/shop/add-to-order.graphql

mutation ($id: ID! $qty: Int!) {
    addItemToOrder(productVariantId: $id quantity: $qty) {
        ...on Order {
            id
            code
            lines {
                id
                quantity
                productVariant {
                    id
                }
            }
        }
        ...on ErrorResult {
            errorCode
        }
    }
}