My answer is that you don't need to buy a key, it's randomly generated when you create a wallet to use. I recommend you need to learn how to use the wallet as well as store the wallet code, the seed code. That's the key to help you get into the current wallet, I think you still don't know how to own it. If you don't know how to use it and don't have the keys, chances are your assets will be locked and you won't be able to use them, move them or sell them.