Twitter cards work by using <meta> tags with names that include a colon: twitter:card, twitter:site, twitter:creator, etc.
The current parsing of ikiwiki's directive doesn't support using colons in names.
This patch fixes it.
Disclaimer: I don't know anything about Perl or the internals of ikiwiki but I managed to "make it work". It might still be flawed in many ways.
Twitter is not really picky about HTML and actually parses <meta> tags outside of the <head> section, so there's currently a workaround.
That's what I did on the donation page of Tails for now.
Hi! Thanks for looking at this. Correct me if I misunderstand your message. I think you are saying that this bug with colons remains in IkiWiki's parser, and you have not fixed that, but you have a a workaround, namely putting the meta tags as HTML into the body of the page? That's a useful workaround and worthy of documenting, but it's not a "patch" so I have removed the patch tag.
If, instead, you have actually got a patch for the IkiWiki parser, please post it and I can take a look: I'm not an IkiWiki maintainer but I can review it and give my opinion at least. If that's the case, please share it, and re-add
[[!tag patch]]. Thanks! —Jon, 2020-10-13