Mrthdrb

passing product id and form key through url but product not added to cart in magento2.

http://127.0.0.1/magento2.3/checkout/cart/add/uenc/aHR0cDovLzEyNy4wLjAuMS9waGlsaXBzX0hVRV8yXzAvZmVlZC9leHBvcnQvZXhlY3V0ZT9jYWxsYmFjaz1qUXVlcnkxMTI0MDM0MDU1MTE2ODg3NTA4NTNfMTU1NDEyNjcxMzYxMyZpZD0xOCZtb2RlPWNvbnRpbnVlJnJhbmQ9MC4wNTYyODUxODIzMTAyODkyMyZfPTE1NTQxMjY3MTM2MTUmaXNBamF4PXRydWU%2C/product/1/form_key/uiYQPpblGQ6hsldy

Magento 2.3 has stopped adding product to cart via GET request. It will only add product to cart if you pass your parameters like product id and other needed parameters in POST. If you are using GET method, it will simply redirect with error message.

As a workaround,you can create your custom module.
Add following 2 files to your custom module.

[Vendor]/[Module]/etc/frontend/routes.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="urn:magento:framework:App/etc/routes.xsd">
 <router id="standard">
 <route id="customaddtocart" frontName="customaddtocart">
 <module name="[Vendor]_[Module]"/>
 </route>
 </router>
</config>

[Vendor]/[Module]/Controller/Cart/Add.php

<?php

namespace [Vendor][Module]ControllerCart;

class AddAction extends MagentoFrameworkAppActionAction

 protected $storeManager;
 protected $cart;
 protected $productRepository;

 public function __construct(
 MagentoFrameworkAppActionContext $context,
 MagentoStoreModelStoreManagerInterface $storeManager,
 MagentoCheckoutModelCart $cart,
 MagentoCatalogModelProductRepository $productRepository
 )
 
 parent::__construct($context);
 $this->storeManager = $storeManager;
 $this->cart = $cart;
 $this->productRepository = $productRepository;
 

 public function execute()
 
 $product_id = $this->getRequest()->getParam('product');
 $product = $this->getProductById($product_id);
 $params = [];
 $params['product'] = $product->getId();
 $params['form_key'] = $this->getRequest()->getParam('form_key');
 $params['qty'] = 1;
 $this->cart->addProduct($product, $params);

 // You can either redirect to some page or return json response from here
 

 public function getProductById($id)
 
 return $this->productRepository->getById($id, false, $this->storeManager->getStore()->getId());
 

Now you can call your controller like, http://yourwebsite.com/customaddtocart/cart/add/product/1/form_key/xxxxx