Your Security Certificate Is Expiring or Broken: How to Fix It
The security certificate is what puts the padlock next to your address. When it expires or breaks, browsers show a full-screen warning and most visitors leave immediately.
Why it happens
Certificates last at most about a year and must be renewed. Most hosting companies renew them automatically, but that automation breaks when a card expires, a setting changes, or the domain moves.
The fix, in most cases
Log in to your hosting control panel and look for "SSL", "Security" or "Certificates". There is usually a button to issue or renew a free certificate (often called Let’s Encrypt). Click it, wait a few minutes, and reload your site.
Turn on automatic renewal
While you are there, make sure auto-renewal is switched on so this never happens again. If your host charges for certificates or cannot auto-renew, that is a sign to consider a better host.
Send every visitor to the secure address
Also enable the "force https" or "always use https" setting, so anyone typing your plain address is moved to the secure one automatically.