How should I track the page author traffic from my website to GA?

I cant find page_author in my GA debugview

I already add parameter in my main tag in GTM
And this is the variable that I am using

When I access the variable in messages, there you have it (the pagePostAuthor

But the value is undefined in the container load

I hope to see page_author (or anything else similar) to show me the traffic that is coming to my website based on the author.