If I make a new org heading, and put the cursor just after the space following the last heading star, then the citar package won't create a new style citation link; if I type C-c b, I get this error message in the minibuffer:
user-error: Cannot insert a citation here
The author of citar tells me that this error comes from org, not the citar package.
However, if I type a single visible character first, then C-c b works. In other words:
I can do this:
*** A [cite:@Kraskov04EstMutInfKNN]
I can't do this:
*** [cite:@Kraskov04EstMutInfKNN]
This is only true for the new cite links. I can put org-ref links at the start of a headline, as well as the old emacs bibtex links.