Hi i think there is a flaw in crypto currency
1. The max supply and circulating supply is the one that makes it unstable. That's why the price value of the coins changes drastically everyday. It makes the payment system very risky to use in our daily cost.
For example: you are going to pay your bills tomorrow, but then the price of your altcoin or bitcoin you are holding fell down big time which greatly affected your money and it can be the reason why you can't pay your bill.
This is the reason why i think crypto currencies are more likely to be stocks rather than a currency itself. The only different thing is that you can send those coin to buy goods
2. There are network issues like bitcoins getting stuck on the network and the transfer time is slow and the fee is very high which makes it inconvinient when paying someone
3. The biggest problem is you also need internet connection for it to work.
Example: lets just say you went to a rural area with no technology or internet connection. There's no way you can send someone your coins by using bluetooth. Crypto currencies are so blockchain dependent, it needs to have something better that can work even offline