I downloaded Portal 2 on PSN and have my PSN account linked to my Steam account. Where do I find the voucher to download the game on Steam?
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I could be wrong on this, but I am about 80% sure the voucher comes with NEW physical copies only. You would have to buy access on Steam, if you bought the digital version on PSN. SOrry.
Again, I could be wrong, but this is most likely the case.