SSL Certificate Errors Explained: Fix HTTPS, Redirect, and Mixed Content Problems

Overview

HTTPS depends on several connected layers: the domain must resolve to the intended server, that server must present a certificate covering the requested hostname, the certificate chain must be trusted by the browser, and the website must consistently use secure URLs. A failure at any layer can produce an SSL certificate warning or make HTTPS appear unavailable.

Start by recording the exact browser message and the affected URL. “Your connection is not private,” “certificate expired,” “certificate name mismatch,” “too many redirects,” and “mixed content” indicate different problems. Test the main domain, the www hostname, and any important subdomains separately because a certificate or server rule may cover one hostname but not another.

Checklist by scenario

When the certificate is expired or invalid

1. Open the hosting panel or certificate management tool and confirm which certificate is assigned to the site.
2. Check the certificate’s validity dates and the hostnames listed on it. Include both the root domain and www if both are used.
3. Review the renewal status. A failed domain-control validation, changed DNS record, disabled automation, or inaccessible validation path can interrupt renewal.
4. Renew or replace the certificate through the hosting provider, certificate manager, or server process used by the site.
5. Install the complete certificate chain when the procedure provides a separate intermediate certificate. The exact fields and terminology vary by hosting panel.
6. Test the public site after installation rather than relying only on the panel’s success message.

When HTTPS is not working after a migration or DNS change

1. Confirm that the domain’s A, AAAA, or relevant CNAME records point to the intended hosting environment. DNS changes can leave users reaching an old server while others reach the new one.
2. Verify that the new server has a certificate for every hostname in use.
3. Check that the server accepts HTTPS connections and that its virtual host or site binding maps the hostname to the correct website.
4. Confirm that the firewall, load balancer, or cloud security rules allow HTTPS traffic.
5. Compare the old and new redirect, proxy, and application URL settings before removing the old configuration.

For a broader move, use a documented website migration checklist and review DNS changes separately with the DNS records guide.

When HTTP-to-HTTPS redirects loop or fail

1. Confirm that HTTPS works directly before creating a redirect. A redirect cannot repair a missing or invalid certificate.
2. Choose one canonical hostname, such as the root domain or www, and define whether the final URL uses HTTPS.
3. Inspect redirect rules in the web server, content management system, plugins, CDN, reverse proxy, and hosting panel. Apply the redirect in one controlled layer where possible.
4. If a proxy terminates TLS before forwarding requests to the origin, ensure the application can correctly detect the original HTTPS request. Otherwise, it may redirect an already secure request back to HTTPS repeatedly.
5. Test both HTTP and HTTPS versions, including the chosen and non-chosen hostnames, using a private browser window or command-line header inspection.

When the browser reports mixed content

1. Open the browser’s developer tools and identify every resource blocked or downgraded from HTTPS.
2. Update hard-coded image, script, stylesheet, font, iframe, API, and media URLs from http:// to https://.
3. Check theme files, templates, database content, JavaScript configuration, third-party embeds, and cached HTML—not only the visible page editor.
4. Replace third-party resources that do not support HTTPS or remove them if they are no longer required.
5. Clear application, page, CDN, and browser caches, then retest representative pages and checkout or login flows.

What to double-check

Certificate installation

• The certificate covers every required hostname and is installed on the server that receives public traffic.
• The server presents the intended certificate, not a default certificate from another virtual host.
• The private key matches the certificate, and access permissions allow the web server to use it.
• The certificate chain is complete and the server configuration has been reloaded where required.

Renewal verification

Do not treat an automated renewal notification as the final check. Visit the live HTTPS endpoint, inspect the certificate dates and names, and confirm that the certificate issuer and chain are accepted by the browsers and clients your audience uses. If renewal depends on DNS or a validation file, make sure future DNS management or deployment changes will not remove that validation path.

Browser and server testing

Test from more than one network or monitoring location when the issue may involve DNS or a CDN. Check the response headers for redirect behavior, inspect the certificate presented by the public endpoint, and test important subdomains such as an API, mail-related web interface, staging hostname, or customer portal. Server logs can reveal which hostname and protocol the application actually receives.

For recurring failures, add certificate-expiry and HTTPS availability checks to your website uptime monitoring process. Monitoring should alert a responsible person before a certificate reaches its renewal deadline, while still treating the live endpoint as the source of truth.

Common mistakes

• Checking only the root domain: A certificate can work for one hostname while www or a subdomain fails.
• Changing DNS and SSL settings at the same time: Make one controlled change at a time so the failure is easier to isolate.
• Adding more redirect rules: Duplicate rules often create loops. First map the request path through the proxy, server, and application.
• Ignoring IPv6: An AAAA record can send some visitors to a server with different HTTPS configuration than the IPv4 destination.
• Assuming a browser cache is the cause: Test the public endpoint and headers before clearing caches or changing application code.
• Using insecure workarounds: Do not tell visitors to bypass certificate warnings or leave login, payment, and administrative pages on HTTP.

When to revisit

Return to this checklist before a certificate renewal window, domain transfer, DNS change, hosting migration, CDN or reverse-proxy change, major CMS update, or redesign. Revisit it after adding a subdomain, changing the canonical hostname, moving an API, or replacing third-party scripts and embeds. These events can alter certificate coverage, validation, redirects, or resource URLs even when the main website appears unchanged.

As a practical final pass, keep a short HTTPS record containing the canonical URLs, certificate owner, renewal method, DNS provider, hosting endpoint, redirect location, and monitoring contact. Test the root domain, alternate hostname, key subdomains, HTTP redirects, certificate dates, and representative pages. If the issue remains unclear, preserve the exact browser error, timestamp, DNS result, redirect chain, and server logs before contacting your hosting provider. That evidence usually makes the difference between a quick configuration fix and repeated trial and error.