Gregory's Server
@glyph One thing to note is that if a link preview has already been generated before it will not update until 2 weeks have passed and the link gets posted again. Have you added the meta tag and saved the permitted domains in your settings before posting the link?
@Gargron no, I posted the link about 10 minutes before I saw this. It's a bit inscrutable to have caching periods that long and no visibility into them. Please consider adding some kind of inspectable metadata somewhere, "preview last generated on" or somesuch, so that site authors can do something more than reloading a lot and hoping