Keys are one of the many items found in Harry Potter: Wizards Unite. You need them to open Portkey Portmanteaus. Silver keys are one-time use only. This means that you need to control how much of them you have to develop your character and visit new parts of the magical world.
If you want to get keys fast, you can get them by spending the in-game gold. One key cost 90 coins, 4 of them cost 325 coins.
Each new level gained gives you a few potions, a bit of gold and a few silver keys. By developing your character, you can keep getting new keys.
Chests in the Registry
Each category in the Register has a few levels. Reach the required level (by collecting enough Foundables) to receive a chest. Inside, you can find up to several keys.
Daily treasures are received every day by logging into the game. The developers have prepared something special for those, who play Harry Potter: Wizards Unite every day. You can get energy, gold, potions, or resources.
Some of the challenges in Harry Potter: Wizards Unite reward you with silver keys. You won't get a lot of them - you can only get 8 if you complete all the available challenges. Despite that, this is yet another way of getting these items.