In Fire Emblem Engage, players are given the option partway through the game to donate to various kingdoms they encounter. However, it is not clear what the benefit of doing so is at first, so players might not understand why they want to spend a lot of money to increase their donation level. Leveling up all four kingdoms may not be worth it for every player, but they may want to focus on one or two depending on what they need most.

https://screenrant.com/fire-emblem-engage-donations-guide-how-to-donate-rewards/