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This warning looks alarming, but it usually traces back to one of a handful of specific, fixable causes.
Expired SSL Certificate
The most common cause. Check your certificate's expiration date in Plesk and renew it — if you're using Let's Encrypt with auto-renewal enabled, this shouldn't happen, but it's worth confirming renewal is actually working.
Certificate Doesn't Match the Domain
If your certificate covers yourdomain.com but visitors reach www.yourdomain.com (or vice versa), the mismatch triggers this warning. Make sure your certificate covers both versions.
Mixed Content Issues
If your HTTPS page loads some resources (images, scripts) over unencrypted HTTP, browsers may flag the page as insecure. Update any hardcoded HTTP links to HTTPS.
Incorrect Server Time
Rarely, a server's system clock being significantly wrong can cause certificate validation to fail, since certificates are time-sensitive.
Visitor-Side Issues
Occasionally the problem isn't your site at all — an outdated browser or incorrect device clock on the visitor's end can trigger the same warning. Ask if the issue is happening on multiple devices before assuming it's server-side.
