The webhook is mainly used for our plugin to receive a notification of the charge from Stripe. Once a subscription is created in your Stripe account, the charge will work fine even without the webhook. So you don’t have to be scared that you will miss a payment or anything.
The notice you are getting usually happens when the URL of the webhook has changed or there is redirect in place. Have you added any 301 redirect to your site (via a plugin or via the htaccess file)? If you go to your Stripe account and check the webhook URL value (in live mode), what value do you see? If you enter that in the browser’s address bar, does it get auto-redirected?
Alos, you can delete the existing webhook URLs in your Stripe account then re-create them using the addon to make sure there is no old URLs that is no longer needed is creating this notice.