Take this as a lesson learned.
Programming the meters and the app to do this is harder than one might think, especially for a government bureaucracy. And look at it this way: What did these replace? They replaced regular old coin meters or time slips - both systems that had no way of telling you not to park. So as far as the upgrade is concerned, you got the new card meters and the convenience of an app - it was a bit foolhardy on your part to just assume some lockout feature would be included if it isn’t expressly stated in any of the documentation or app terms.
Not saying it doesn’t suck, but it doesn’t really help your defense, sorry to say. Not saying you can’t try fighting it, you have your time to lose only. I don’t think the “didn’t know event is happening” is strong either, since the onus is on you to call or lookup. Ignorance is virtually never an effective defense.
City parking is a racket, but Pittsburgh is better than most. Heaven help you if you try to park in NYC without reading all the rules. They don’t give a shit. And even if a meter is broken, it is your responsibility to check the other side of the street if there is one in the same block and then still your responsibility to call 311 - without this you won’t have a defense.