ReflectionException: Class “” does not exist ServiceInputProcessor.php

Been stuck for days trying to figure out the reason but I can’t locate it.

API always returns an error when I open the cart or add to the cart

main.CRITICAL: ReflectionException: Class "" does not exist in /var/www/vhosts/example.com/public_html/vendor/magento/framework/Webapi/ServiceInputProcessor.php:278
Stack trace:
#0 /var/www/vhosts/example.com/public_html/vendor/magento/framework/Webapi/ServiceInputProcessor.php(278): ReflectionClass->__construct()
#1 /var/www/vhosts/example.com/public_html/vendor/magento/framework/Webapi/ServiceInputProcessor.php(524): MagentoFrameworkWebapiServiceInputProcessor->_createFromArray()
#2 /var/www/vhosts/example.com/public_html/vendor/magento/framework/Webapi/ServiceInputProcessor.php(200): MagentoFrameworkWebapiServiceInputProcessor->convertValue()
#3 /var/www/vhosts/example.com/public_html/vendor/magento/module-webapi/Controller/Rest/InputParamsResolver.php(115): MagentoFrameworkWebapiServiceInputProcessor->process()
#4 /var/www/vhosts/example.com/public_html/vendor/magento/framework/Interception/Interceptor.php(58): MagentoWebapiControllerRestInputParamsResolver->resolve()
#5 /var/www/vhosts/example.com/public_html/vendor/magento/framework/Interception/Interceptor.php(138): MagentoWebapiControllerRestInputParamsResolverInterceptor->___callParent()
#6 /var/www/vhosts/example.com/public_html/vendor/magento/framework/Interception/Interceptor.php(153): MagentoWebapiControllerRestInputParamsResolverInterceptor->MagentoFrameworkInterception{closure}()
#7 /var/www/vhosts/example.com/public_html/generated/code/Magento/Webapi/Controller/Rest/InputParamsResolver/Interceptor.php(23): MagentoWebapiControllerRestInputParamsResolverInterceptor->___callPlugins()
#8 /var/www/vhosts/example.com/public_html/vendor/magento/module-webapi/Controller/Rest/SynchronousRequestProcessor.php(85): MagentoWebapiControllerRestInputParamsResolverInterceptor->resolve()
#9 /var/www/vhosts/example.com/public_html/vendor/magento/module-webapi/Controller/Rest.php(188): MagentoWebapiControllerRestSynchronousRequestProcessor->process()
#10 /var/www/vhosts/example.com/public_html/vendor/magento/framework/Interception/Interceptor.php(58): MagentoWebapiControllerRest->dispatch()
#11 /var/www/vhosts/example.com/public_html/vendor/magento/framework/Interception/Interceptor.php(138): MagentoWebapiControllerRestInterceptor->___callParent()
#12 /var/www/vhosts/example.com/public_html/vendor/magento/framework/Interception/Interceptor.php(153): MagentoWebapiControllerRestInterceptor->MagentoFrameworkInterception{closure}()
#13 /var/www/vhosts/example.com/public_html/generated/code/Magento/Webapi/Controller/Rest/Interceptor.php(23): MagentoWebapiControllerRestInterceptor->___callPlugins()
#14 /var/www/vhosts/example.com/public_html/vendor/magento/framework/App/Http.php(116): MagentoWebapiControllerRestInterceptor->dispatch()
#15 /var/www/vhosts/example.com/public_html/generated/code/Magento/Framework/App/Http/Interceptor.php(23): MagentoFrameworkAppHttp->launch()
#16 /var/www/vhosts/example.com/public_html/vendor/magento/framework/App/Bootstrap.php(264): MagentoFrameworkAppHttpInterceptor->launch()
#17 /var/www/vhosts/example.com/public_html/pub/index.php(30): MagentoFrameworkAppBootstrap->run()
#18 {main}

The custom webapi.xml file

<?xml version="1.0"?>
<routes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Webapi:etc/webapi.xsd">
    <!-- <route url="/V1/carts/:cartId/updateCart" method="POST">
        <service class="TAGCartManagerApiCartManagementInterface" method="updateCart"/>
            <resources>
                <resource ref="Magento_Cart::manage"/>
            </resources>
    </route> -->

    <route url="/V2/get-details" method="GET">
        <service class="NewCustomApiApiDetailsInterface" method="getData" />
        <resources>
            <!-- <resource ref="anonymous" /> -->
            <resource ref="self" />
        </resources>
    </route>

    <route url="/V2/customer/login" method="POST">
        <service class="NewCustomApiApiCustomerInterface" method="login" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V2/customer/login/socialmedia" method="POST">
        <service class="NewCustomApiApiCustomerInterface" method="loginWithSocialMedia" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V2/customer/logout" method="POST">
        <service class="NewCustomApiApiCustomerInterface" method="logout" />
        <resources>
            <resource ref="self" />
        </resources>
        <data>
            <parameter name="customerId" force="true">%customer_id%</parameter>
        </data>
    </route>
    <route url="/V2/customer/me/profile" method="GET">
        <service class="MagentoCustomerApiCustomerRepositoryInterface" method="getById" />
        <resources>
            <resource ref="self" />
        </resources>
        <data>
            <parameter name="customerId" force="true">%customer_id%</parameter>
        </data>
    </route>
    <route url="/V2/customer/me/profile" method="PUT">
        <service class="MagentoCustomerApiCustomerRepositoryInterface" method="save" />
        <resources>
            <resource ref="self" />
        </resources>
        <data>
            <parameter name="customer.id" force="true">%customer_id%</parameter>
        </data>
    </route>
    <route url="/V2/customer/registration" method="POST">
        <service class="MagentoCustomerApiAccountManagementInterface" method="createAccount" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V2/customer/registration/socialmedia" method="POST">
        <service class="NewCustomApiApiCustomerInterface" method="createAccountWithSocialMedia" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V2/customer/resetPassword" method="POST">
        <service class="MagentoCustomerApiAccountManagementInterface" method="resetPassword" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V2/customer/rest/password" method="PUT">
        <service class="MagentoCustomerApiAccountManagementInterface" method="initiatePasswordReset" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <route url="/V2/customer/changePassword" method="PUT">
        <service class="MagentoCustomerApiAccountManagementInterface" method="changePasswordById"/>
        <resources>
            <resource ref="self"/>
        </resources>
    </route>

    <route url="/V2/customer/saveAddress" method="POST">
        <service class="MagentoCustomerApiAddressRepositoryInterface" method="save"/>
        <resources>
            <resource ref="self"/>
        </resources>
    </route>

    <route url="/V2/customer/deleteAddress" method="DELETE">
        <service class="MagentoCustomerApiAddressRepositoryInterface" method="deleteById"/>
        <resources>
            <resource ref="self"/>
        </resources>
    </route>

    <!-- Products Functions -->

    <!-- get all products details -->
    <route url="/V2/products" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getList" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- search products -->
    <route url="/V2/searchProducts" method="GET">
        <service class="MagentoCatalogApiProductRepositoryInterface" method="getList" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <route url="/V2/products/search/:value" method="GET">
        <service class="NewCustomApiApiProductInterface" method="searchProducts" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get product details by product id -->
    <route url="/V2/products/:id" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getProductById" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V2/products/instock" method="GET">
        <service class="NewCustomApiApiProductInterface" method="isInStock" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get product details by product sku -->
    <route url="/V2/products/sku" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getProductBySku" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get configurable product details -->
    <route url="/V2/configurable-products/:sku/details" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getProductConfigurableDetails" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get configurable product children -->
    <route url="/V2/configurable-products/:sku/children" method="GET">
        <service class="MagentoConfigurableProductApiLinkManagementInterface" method="getChildren" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get configurable product options -->
    <route url="/V2/configurable-products/:sku/options" method="GET">
        <service class="MagentoConfigurableProductApiOptionRepositoryInterface" method="getList" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get configurable product details -->
    <route url="/V2/bundle-products/:sku/details" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getProductBundleDetails" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get bundle product children -->
    <route url="/V2/bundle-products/:productSku/children" method="GET">
        <service class="MagentoBundleApiProductLinkManagementInterface" method="getChildren" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get bundle product options -->
    <route url="/V2/bundle-products/:sku/options" method="GET">
        <service class="MagentoBundleApiProductOptionRepositoryInterface" method="getList" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get Featured products -->
    <route url="/V2/products/featured" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getFeaturedProducts" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get Best Seller products -->
    <route url="/V2/products/bestseller" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getBestSellersProducts" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get Special Offer products -->
    <route url="/V2/products/specialoffer" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getSpecialOfferProducts" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get product attributeId by code-->
    <route url="/V2/products/attributeid/:attrCode" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getAttributeId" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get product attributevalue by valueIndex-->
    <route url="/V2/products/attributevalue/:attrId" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getAttributeValue" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get categories tree -->
    <route url="/V2/categoriestree" method="GET">
        <service class="MagentoCatalogApiCategoryManagementInterface" method="getTree" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get categories -->
    <route url="/V2/categories" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getCategories" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>


    <!-- get product details by category id -->
    <route url="/V2/categories/:categoryId/products" method="GET">
        <service class="NewCustomApiApiProductInterface" method="getCategoryProducts" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>


    <!-- Checkout APIs -->

    <!-- Create empty cart for guest-->
    <route url="/V2/checkout/createGuestCart" method="POST">
        <service class="MagentoQuoteApiCartManagementInterface" method="createEmptyCart" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- Create empty cart for customer-->
    <route url="/V2/checkout/:customerId/cart" method="POST">
        <service class="NewCustomApiApiCheckoutInterface" method="createCustomerEmptyCart" />
        <resources>
            <resource ref="self" />
        </resources>
    </route>

    <!-- add to cart -->
    <route url="/V2/checkout/cart/add" method="POST">
        <service class="MagentoQuoteApiCartItemRepositoryInterface" method="save" />
        <resources>
            <resource ref="anonymous" />
        </resources>
        <data>
            <parameter name="cartId" force="true">%cart_id%</parameter>
        </data>
    </route>

    <!-- override cart -->
    <route url="/V2/checkout/cart/:cartId/add/:itemId" method="PUT">
        <service class="MagentoQuoteApiCartItemRepositoryInterface" method="save" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- remove from cart -->
    <route url="/V2/checkout/cart/:cartId/delete" method="DELETE">
        <service class="MagentoQuoteApiCartItemRepositoryInterface" method="deleteById" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V2/checkout/cart/:cartId/deleteAll" method="DELETE">
        <service class="NewCustomApiApiCheckoutInterface" method="removeCartItems" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <!-- get cart items -->
    <route url="/V2/checkout/cart/:cartId/items" method="GET">
        <service class="NewCustomApiApiCheckoutInterface" method="getCartItems" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- override cart by product id-->
    <route url="/V2/checkout/cart/overridebyproduct" method="PUT">
        <service class="NewCustomApiApiCheckoutInterface" method="overrideCartItemByProductId" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get cart totals -->
    <route url="/V2/checkout/cart/:cartId/totals" method="GET">
        <service class="NewCustomApiApiCheckoutInterface" method="getCartTotals" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- assign cart to customer -->
    <route url="/V2/checkout/assigncustomer/:cartId" method="PUT">
        <service class="NewCustomApiApiCheckoutInterface" method="assignCustomer" />
        <resources>
            <resource ref="self" />
        </resources>
    </route>

    <!-- get shipment method based on address -->
    <route url="/V2/checkout/shipping-information/:cartId/methods" method="POST">
        <service class="MagentoQuoteApiShipmentEstimationInterface" method="estimateByExtendedAddress" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- save shipping information -->
    <route url="/V2/checkout/shipping-information/:cartId/save" method="POST">
        <service class="NewCustomApiApiCheckoutInterface" method="saveAddressInformation" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- Managing shipping guest information -->
    <!--<route url="/V2/checkout/guest-carts/shipping-information/:cartId/save" method="POST">-->
    <!--    <service class="NewCustomApiApiCheckoutInterface" method="saveGuestAddressInformation"/>-->
    <!--    <resources>-->
    <!--        <resource ref="anonymous" />-->
    <!--    </resources>-->
    <!--</route>-->

    <!-- apply shipping information -->
    <route url="/V2/checkout/shipping-information/:cartId/applymethod" method="POST">
        <service class="NewCustomApiApiCheckoutInterface" method="set" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- Place Order -->
    <route url="/V2/checkout/placeOrder" method="PUT">
        <service class="NewCustomApiApiCheckoutInterface" method="placeOrder" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <route url="/V2/checkout/orders" method="GET">
        <!-- <service class="MagentoSalesApiOrderRepositoryInterface" method="getList" /> -->
        <service class="NewCustomApiApiCheckoutInterface" method="getOrders"/>
        <resources>
            <resource ref="self" />
        </resources>
    </route>

    <route url="/V2/checkout/defaultcountry" method="GET">
        <service class="NewCustomApiApiCheckoutInterface" method="getDefaultCountryCode" />
        <resources>
            <resource ref="self" />
        </resources>
    </route>
    <route url="/V2/checkout/regions/:countryCode" method="GET">
        <service class="NewCustomApiApiCheckoutInterface" method="getRegions" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <!-- start custom for example.com -->
    <route url="/V2/checkout/cities/:regionId" method="GET">
        <service class="NewCustomApiApiCheckoutInterface" method="getCities" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V2/checkout/areas/:cityId" method="GET">
        <service class="NewCustomApiApiCheckoutInterface" method="getAreas" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <!-- end custom for example.com -->

    <!-- Wishlist APIs -->
    <route url="/V2/wishlist/items" method="GET">
        <service class="NewCustomApiApiWishlistManagementInterface" method="getWishlistForCustomer" />
        <resources>
            <resource ref="self" />
        </resources>
    </route>
    <route url="/V2/wishlist/add/:productId" method="POST">
        <service class="NewCustomApiApiWishlistManagementInterface" method="addWishlistForCustomer" />
        <resources>
            <resource ref="self" />
        </resources>
    </route>

    <route url="/V2/wishlist/remove/:itemId" method="DELETE">
        <service class="NewCustomApiApiWishlistManagementInterface" method="removeWishlistItem" />
        <resources>
            <resource ref="self" />
        </resources>
    </route>

    <route url="/V2/wishlist/removeAll/:customerId" method="DELETE">
        <service class="NewCustomApiApiWishlistManagementInterface" method="removeWishlistItems" />
        <resources>
            <resource ref="self" />
        </resources>
    </route>
    <route url="/V2/wishlist/remove/:itemId" method="DELETE">
        <service class="NewCustomApiApiWishlistManagementInterface" method="removeWishlistItem" />
        <resources>
            <resource ref="self" />
        </resources>
    </route>

    <route url="/V2/wishlist/item/in" method="GET">
        <service class="NewCustomApiApiWishlistManagementInterface" method="isProductInWishlist" />
        <resources>
            <resource ref="self" />
        </resources>
    </route>

    <!-- add to cart -->
    <route url="/V2/wishlist/addAllCart" method="POST">
        <service class="NewCustomApiApiWishlistManagementInterface" method="addAllToCart" />
        <resources>
            <resource ref="self" />
        </resources>
    </route>

    <!-- GENERAL -->

    <route url="/V2/currencies" method="GET">
        <service class="MagentoDirectoryApiCurrencyInformationAcquirerInterface" method="getCurrencyInfo"/>
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get general information -->
    <route url="/V2/general/information" method="GET">
        <service class="NewCustomApiApiGeneralInterface" method="getGeneralInformation" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get banners -->
    <route url="/V2/general/banners" method="GET">
        <service class="NewCustomApiApiGeneralInterface" method="getBannersBySlider" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get CMS page content -->
    <route url="/V2/general/pageContent" method="GET">
        <service class="NewCustomApiApiGeneralInterface" method="getCmsPageDetails" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <!-- get CMS block content -->
    <route url="/V2/general/blockContent" method="GET">
        <service class="NewCustomApiApiGeneralInterface" method="getCmsBlockDetails" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <route url="/V2/general/featuredcategories" method="GET">
        <service class="NewCustomApiApiGeneralInterface" method="getFeaturedSubCategories" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <route url="/V2/general/advertisement" method="GET">
        <service class="NewCustomApiApiGeneralInterface" method="getAdvertisement" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <route url="/V2/general/supplier" method="GET">
        <service class="NewCustomApiApiGeneralInterface" method="getSupplier" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <route url="/V2/general/contactus" method="GET">
        <service class="NewCustomApiApiGeneralInterface" method="getContactUsDetails" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <route url="/V2/general/sociallinks" method="GET">
        <service class="NewCustomApiApiGeneralInterface" method="getSocialLinks" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

    <route url="/V2/general/homeproducts" method="GET">
        <service class="NewCustomApiApiGeneralInterface" method="getHomeProducts" />
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>

</routes>

Method to get cart items

/**
 * {@inheritdoc}
 */
public function getCartItems($cartId, $currencyCode)
{
    $response = [];
    $list = $this->cartItemRepository->getList($cartId);
    $items = [];

    $objectManager = MagentoFrameworkAppObjectManager::getInstance();
    $mediaPath = $objectManager->get('MagentoStoreModelStoreManagerInterface')
        ->getStore()
        ->getBaseUrl(MagentoFrameworkUrlInterface::URL_TYPE_MEDIA);

    $totalQty = 0;
    foreach ($list as $item) {
        $data = [];
        $data['item_id'] = $item->getItemId();
        $data['id'] = $item->getProduct()->getId();
        $data['name'] = $item->getName();
        $data['qty'] = $item->getQty();
        $data['sku'] = $item->getSku();

        $data['price'] = $this->helper->convertPriceFromCurrentToAnotherCurrency($item->getPrice(), $currencyCode);


        $image = $item->getProduct()->getData("image");
        if ($image == null || $image == '')
            $image = $item->getProduct()->getData("thumbnail");

        if ($image != null && $image != '')
            $data['image'] = $mediaPath . "catalog/product" . $item->getProduct()->getData("thumbnail");
        else
            $data['image'] = '';

        $items[] =  $data;
        $totalQty += $item->getQty();
    }

    $response['items'] = $items;
    $response['count'] = count($list);
    $response['total_qty'] = $totalQty;
    return [$response];
}