The SSL certificate for meta.gis.stackexchange.com expired on 2020-09-06. Also, it is not valid for that domain...
The domain is apparently only a redirect to gis.meta.stackexchange.com, which has a correct certificate.
It has never been valid for that domain, because it's not possible to request a wildcard domain for meta.*.stackexchange.com
. This is the main reason they switched to https://gis.meta.stackexchange.com during the great HTTP → HTTPS migration: Network-wide HTTPS: It's time.
There should be no links in the system pointing to https://meta.gis.stackexchange.com, as that domain never was accessible via HTTPS. Its HTTP equivalent, http://meta.gis.stackexchange.com, properly redirects to this Meta site (in HTTPS). If you do see a link to https://meta.gis.stackexchange.com or its subpages, it must be because someone made an error.
The certificate is valid for the *.stackexchange.com domain
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As a moderators are volunteers not employees.