Cannot purchase VoH on PS5 when using disc for D4

I have the disc version of Diablo 4 on PS5. I made a spiritborn and am loving it, so I decided to buy VoH so that I can keep playing once this free trial thing is over. When I go into the store, it says VoH is unavailable. It has a $20 upgrade to the deluxe version, but not the base expansion. The game knows I don’t have the expansion because it wont let me use pets (says I am missing VoH). I would like to get the expansion while it is on sale. I tried on the PS5, via the playstation app, and on the playstation website. Is this happening because of this free trial thing that is currently going on?