I had done it before as your post said. All I found is a PS5 version item which I have to pay for it. So I Google for a solution. Unfortunately, I found nothing. And then I posted the question here for answers.
Unfortunately again. Your answer does not match the reality of the PS store. PS4 version owners like me have to pay again to get the PS5 version.
I hope you check your account on the PS store to verify it.
If it is a bug on the PS store. Please fix it.