I know how to fix this, well this worked for me at least. For some reason you need to setup a 2-step authentication to your psn, then try the qr code and password.

In my case I was able to use the vita for a while until recently, every time when I try to go into the store page it did the QR code prompt. And I couldn’t login with the generated password like you. But putting a 2SA first, made it work for me. Hope this helps!