Updated: 14/05/14
A full trailer has been released, revealing the gameplay and campaigns featured in Left 4 Dead: Survivors will actually appear largely the same to that of the original game. Four new exclusive characters have also been revealed, who will likely remain exclusive to this Japanese...
So I purchased the pack (loving the maps so far), but I think I figured out the source of the glitch you encountered. Since Operation Payback is an in-app purchase, it requires you to add money to your Steam Wallet, and the minimum increment you can add is $5.
Thanks! It may be a glitch, as the Counter-Strike blog and Steam page for CS:GO both say it should be $2.99 right now. I'll edit the post and note that you pointed it out. I haven't purchased it yet myself, but I definitely will this weekend.
From now until July 31st, seven of the top-rated Steam Workshop maps will be available on official CS:GO Classic Casual servers through Operation Payback, available now through an in-game purchase for a limited-time discounted price of $2.99, or $5.99 after the offer expires.
The seven maps...