Magento – Magento 2: Requested store is not found in product

You need to run the following query in your database, and then try to open the website.

SET FOREIGN_KEY_CHECKS=0;
UPDATE `store` SET store_id = 0 WHERE code='admin';
UPDATE `store_group` SET group_id = 0 WHERE name='Default';
UPDATE `store_website` SET website_id = 0 WHERE code='admin';
UPDATE `customer_group` SET customer_group_id = 0 WHERE customer_group_code='NOT LOGGED IN';
SET FOREIGN_KEY_CHECKS=1;

Check with following. This is working for me to add custom attribute -

A2bizz/Example/Setup/InstallData.php

namespace A2bizz\Example\Setup;

use Magento\Framework\Setup\InstallDataInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;
use Magento\Framework\Setup\ModuleContextInterface;

class InstallData implements InstallDataInterface {

    private $_eavSetupFactory;
    private $_attributeRepository;

    public function __construct(
        \Magento\Eav\Setup\EavSetupFactory $eavSetupFactory,
        \Magento\Eav\Model\AttributeRepository $attributeRepository
    )
    {
        $this->_eavSetupFactory = $eavSetupFactory;
        $this->_attributeRepository = $attributeRepository;
    }

    public function install( ModuleDataSetupInterface $setup, ModuleContextInterface $context )
    {

        $eavSetup = $this->_eavSetupFactory->create(['setup' => $setup]);

        // add customer_attribute to customer
        $eavSetup->removeAttribute(\Magento\Customer\Model\Customer::ENTITY, 'customer_attribute');
        $eavSetup->addAttribute(
        \Magento\Customer\Model\Customer::ENTITY, 'customer_attribute', [
            'type' => 'varchar',
            'label' => 'Custom Customer Attribute',
            'input' => 'text',
            'required' => false,
            'system' => 0,
            'global' => \Magento\Eav\Model\Entity\Attribute\ScopedAttributeInterface::SCOPE_STORE,
            'sort_order' => '200'
        ]
    );

    // allow customer_attribute attribute to be saved in the specific areas
    $attribute = $this->_attributeRepository->get('customer', 'customer_attribute');
    $setup->getConnection()
    ->insertOnDuplicate(
        $setup->getTable('customer_form_attribute'),
        [
            ['form_code' => 'adminhtml_customer', 'attribute_id' => $attribute->getId()]
        ]
    );
    }
}