I have all goods required for the next Advancement, but the game still asks me to pay Diamonds!

In addition to the goods, your Settlement also requires you to have a certain level of Diplomacy to unlock an advancement. Diplomacy is generated by Diplomacy-Buildings, such as the Runestone (Vikings) and Tōrō (Feudal Japan). If you do not have the diplomacy required, you can use Diamonds to ignore the requirement and unlock it right away. Otherwise, please build more Diplomacy buildings.

Vikings - Small Diplomacy	Feudal Japan - Small Diplomacy	Ancient Egypt - Small Diplomacy	Aztecs - Small Diplomacy	Mughal Empire - Small Diplomacy
Vikings - Large Diplomacy	Feudal Japan - Large Diplomacy	Ancient Egypt - Large Diplomacy	Aztecs - Large Diplomacy	Mughal Empire - Large Diplomacy