Your session has been expired when item added to cart at cart page in magento2

When I was trying to add products on cart in magento2, but it showing an error. :(

This error is occurs when form key is not valid.

if (!$this->_formKeyValidator->validate($this->getRequest())) {
            $this->messageManager->addErrorMessage(
                __('Your session has expired')
            );
            return $this->resultRedirectFactory->create()->setPath('*/*/');
        } 

You should check form key is exist or not in Add to cart request. problem is due to this form key.

Also try these solutions as well

Yes, use 127.0.0.1 instead of localhost

UPDATE `core_config_data` SET `value` = 'http://127.0.0.1/magento/' WHERE `core_config_data`.`path` = 'web/unsecure/base_url';
UPDATE `core_config_data` SET `value` = 'http://127.0.0.1/magento/' WHERE `core_config_data`.`path` = 'web/secure/base_url';

I hope it will helpful for you.