If there is an error "Server error (403)" during saving draft/publishing or other actions in website builder, it can happen due to the following reasons:

• Your website builder session has expired. The session in website builder should never expire when you edit website. However, there are few cases when it can happen:
• someone else opened website builder with your website from your account of hosting control panel. This action leads to your session expiration and new session establishing for another person.
• you opened website builder one more time for the same website in another browser or in incognito window. This action leads to session expiration of first window and new session establishing for new window. To avoid this in the future, we recommend you to have only one website builder window opened at one time.
• you left website builder window opened for a long time and your computer went to sleep or darkened screen. This can lead to limited browser activity for opened windows and prevent website builder from refreshing session.

Unfortunately, if session expires it means that all your changes made after last draft saving in website builder will be lost. To continue editing website in website builder, you need to open website builder again from hosting control panel.

• (Only for On-Premises brand) Builder is facing temporary server problems. During saving draft/publishing website a big set of data is sent to server. Sometimes, servers can have some active POST filters that scan all data by some criteria and can block request to server if needed.
  To fix this issue, contact your hosting provider (or website builder administrator) and tell about this problem.