Hello @Graham Glover
If you have a website at yourdomain.com, the common name on your SSL certificate would be yourdomain.com. So as the error message states, the root problem behind NET::ERR_CERT_COMMON_NAME_INVALID is that the common name on your SSL certificate is not valid for some reason.
The most basic cause of the NET::ERR_CERT_COMMON_NAME_INVALID error is that your site’s domain doesn’t match the common name listed on your SSL certificate. So, the first fix you’ll want to try is viewing your certificate to determine if it’s been misconfigured.
Check the details of your SSL certificate( Secured and Unsecured requests), The domain listed here should match the one you’re trying to reach. If not, you’ll know your certificate is misconfigured.
If the site you’re trying to access uses a SAN certificate, you may need to do some further digging when verifying the SSL certificate in your browser.click on Details in the certificate window Scroll down until you find the section labelled Extension Subject Alternative Name. Below it, you should see a list of all the domains the certificate protects and you should find your custom domain. If not, you’ll know your certificate is misconfigured.
Hope this was helpful. Please let us know in case of any additional questions or concerns.
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