You get links that look like this:

\define wikipediaLink(articleName, linkText)
[[$linkText$|https://en.wikipedia.org/wiki/$articleName$]]
\end

<$macrocall $name="wikipediaLink" linkText="<<linktext>>" articleName="Aardvark" />

In other words, TiddlyWiki did not expand the macro.

Putting quotation marks around a macro call or variable reference passed to an HTML attribute makes it literal – that is, TiddlyWiki doesn't try to look at it to see if it's a variable or macro call. This is very occasionally what you want, but usually it's a mistake.

The quotation marks should be omitted even if the macro call has spaces in it. So for some made-up macro mymacro with two parameters, this would the correct way to call it, even though it may look wrong at first glance:

<$macrocall $name="wikipediaLink" linktext=<<mymacro attribute1 "attribute two">> articleName=Dingo/>