Message from George L. reminds me about something I'll wanted to do (nice to have), adding a card should work like a toggle at least to add card, and have an extra dialog only when removing the card
even just removing the pop up 'add card' and confirmation window would be good -- you could make it so that you can just click 'add card' and it will turn the button into a confirmation/reverse action button in one click.
Message from George L. reminds me about something I'll wanted to do (nice to have), adding a card should work like a toggle at least to add card, and have an extra dialog only when removing the card