I have heard it is permissible to do money exchange business for example you can change dollars to pounds and if one currency goes up you can sell it and make a profit. I’ve also heard that you have to do the transaction hand to hand and that the same currency can’t be exchanged.

Now my question is if the exchange has to take place hand to hand, how can I change a big sum of money for example a million dollars because its not safe to carry out money like this and its not feasible to carry a big amount of money in your hands. So my question is, if i do it through a bank is it halal? Since the bank will exchange the money instantly and convert it but i wont be there to receive it by hand but i will still get it immediately and the money will be available in my bank account