If you don't renew your domain, it will eventually expire. This means your website and any email addresses associated with that domain will stop working.
If you lose ownership of your domain name, it can become available for anyone to purchase, including your competitors. If this happens, you may lose access to your online presence completely.
If your payment method has expired in your account, your network provider should contact you advising you to update to a new payment method. We recommend doing so as soon as you are notified in order to prevent any website downtime from occurring. We also recommend adding a backup payment method to your account.