I have two Mediawiki 1.32 installations running on Ubuntu 16.04, using Apache2, and MySQL. They are both SSL access only with http->https redirect configured in the apache config.
I've set up interwiki links successfully, with the hope of utilizing the Interwiki Transclusion described on this page and others.
A:B Example:
A is source wiki for transcluded content, B is destination.
Wiki A interwiki prefix is "isw", Wiki B is "psw". Interwiki links such as [[isw:Example]] and [[psw:Example2]] work just fine, as expected.
I do have the "Transclude" checkbox set to Yes on Special:Interwiki configuration for BOTH of these Wikis.
Transclusion does work as expected for pages within each wiki. I.E., {{:WikiAPage}} transcludes properly on Wiki A, and {{:WikiBPage}} transcludes properly on Wiki B.
Page "Example" on Wiki A includes an <includeonly> section that I wish to send over to Wiki B using {{isw:Example}} syntax written into Wiki B.
When saving the page on Wiki B with only {{isw:Example}} in the page, I get the following rendered on the page itself, not in an error log or elsewhere.
[Template fetch failed for https://wiki.mydomain.com/wiki/Example?action=render: HTTP 0]
Another interesting detail to include is that when I manually copy and follow that link above, I do get a nice render. "https://wiki.mydomain.com/wiki/Example?action=render" shows a rendered page as I'd expect, in my browser, but NOT included in Wiki B's frame.
What might I be missing here? Thanks for reading!