I just accidentally wasted 50,000 metal on promoting the Machine Gunner to level 2. It sucks that there isn't a confirmation button on a game that is touch screen controlled!
But hey, whatever that's life. The real kicker is the component ticker reset from 12/10 to 2/20 and now I CANNOT even build the stupid units to use in my attacks until I find 18 more component cards.
How is it possible to promote something that I cannot even now build???