Diamond Bank is a safe that keeps the diamonds you have earned in it. It fills with the diamonds you have collected from the goals you scored in your winning matches. Starting from the first level, you can see how many diamonds you have collected for your Diamond Bank after each match you have won. You need to be at least level 20 to unlock the Diamond Bank.
You can collect your Diamonds from the Diamond Bank when it reaches %50 of its capacity. Also, you can just wait for it to fill up and get even more Diamonds.
Once your Diamond Bank is full, you will have 48 hours before you collect your Diamonds. If you don’t open it in 48 hours, the Diamond Bank gets reset, and you lose all the Diamonds you had collected.
Your Diamond Bank will level up as you keep collecting your Diamonds. After each level up, you can save more Diamonds in the Diamond Bank and collect more Diamond per goal. First-level Diamond Bank will be free to collect, but the rest will require a purchase. The highest level you can reach for your Diamond Bank is 10.