Copper Shortage is a quest unlocked as soon as the player has completed Defeat Undead.
The objective is once again to enter the Resource Quarry and harvest resources, but this time Copper instead of Amethyst or Lumber.
Click on the [Harvest] button -> Enter the Resource Quarry to harvest [Copper] x10. Your Blacksmiths require copper to produce weapons. Visit the copper mines to address this issue.