SSL Certificate is invalid or missing intermediate (bundle) certificate

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SSL checker shows "certificate not trusted" warning

When you check your InfinityFree SSL certificate with online SSL checker tools, you might see a warning like this: The certificate is not trusted in all web browsers. You may need to install an Intermediate/chain certificate to link it to a trusted root certificate. This warning sounds scary, but it’s actually not a problem for your website visitors. What this warning means for your site You can safely ignore this warning. Your site will work perfectly fine with HTTPS for virtually all mode…

You can also use CloudFlare

How to setup Full SSL with Cloudflare

By default, Cloudflare uses a system called “Flexible SSL”. In this system, Cloudflare secures the connection between your visitors and Cloudflare, but not the connection between Cloudflare and your website. Not only is this less secure, some websites (notably WordPress) have trouble detecting whether HTTPS is in use, causing all sorts of issues. The best way to resolve this is by using Full SSL in Cloudflare. This way, the connection between Cloudflare and your website is encrypted, and your w…

Anyway there is no issue