It has happened to me again. I used my so valued NPC card, because it doesn't ask me if i'm sure. I just wanted to upgrade a building, but the 3 split made me NPC it. REALLY ANNOYING
Can you add a warning like the gold usage, because a card for me is just as valuable as gold

Are you sure you want to use CARD. Like the gold message!
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aargh...It happens to me all the time as well, especially that finish upgrade early button, it's so annoying
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Same here. I've wasted so much gold just by accidentally NPC'ing the building instead of upgrading it.
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I thought it was just me doing this repeatedly.
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Soon we're going to implement a new setting that will let you choose if you want to receive a confirmation popup a) in no case, b) when using gold, or c) when using an item or gold.