I see. Hve you looked at this?:
https://support.playstation.com/s/article/PS4-Trouble-With-Downloadable-Content?language=en_US
I have looked at that. For some reason, it doesn't show the add-ons that I already have. It only shows the add-on that was released today.
However, looking in my notifications, it shows that the add-on that I am having an issue with is installed.
I am uninstalling and reinstalling the game to see if that helps.