The Bank has limited capacity, which depends on the perks that you have in game (Bank vault NFTs). Default Bank capacity is 100k coins.
Each Bank Vault NFT increases your bank capacity by 20k coins.
Each Bank Vault saves 10% of your coins from possible loss during defense in PVP Battles.
Maximum amount of bank vaults which could be applied is 3 per 1 player. Only 3 bank vaults will take effect on your game even if you will have more than 3 bank vaults.