I have had this problem all afternoon, I have been trying to purchase Doctor who the eternity clock but it comes up with the error code 80023163
seems like everyone is having this problem tonigh...whether they r in EU or AUS...the US doesn't seem to be having this problem...maybe it has to do with the maitenence???
Had the same issue just after adding a €20 Card. Had to do the old IT Crowd thing and turn the PS off and on again. No issues since then with purchasing.
I have been selecting Buy Now rather than Add to Cart. Seems to be a Cart issue, so would recommend just using Buy Now. Might take a tad bit longer for multiple purchases, but at least you'll get your stuff.