Hi @vixal9621 ,
When you encounter the critical errors, it means something in your server gets lost or the site could not establish a connection to the server to process the request to buy the product instantly.
Your site is using an external plugin to make sure customers register an account or login to purchase so it might also interfere with our plugin as well. Our plugin allows customers to quickly skip the cart page and go straight to the checkout so it might be a conflict.
You can test by deactivating other plugins, only keep WooCommerce and our plugin to see if the critical errors go away. Then reactivate others to find when they happen again.
Best regards.