Can’t Make Primary Author Appear 1st

My client has a book written by two authors. I have designated the author I would like to appear first as ‘primary author’ in the plugin, but despite this the author who is not the primary author is listed as the primary author. This can cause professional offence so I am contemplating listing the book as having no authors and thus forcing readers to look at the book cover to see the authorship.

How can I get the primary author to be listed first on the website page?