What is the ruling on dealing with a brokerage firm that gives margin in exchange for a fixed commission on the currency difference, without interest on holding the contract overnight?

The broker in the stock market acts as an agent for the buyer or speculator, and it is permissible for him to take a known fee for each buying and selling transaction. It is forbidden for the broker to take interest on a loan he provides to the client under the margin system. Any increase in the client's capital resulting from price differences is the property of the client, not the broker. If the brokerage firm adheres to these rulings, then there is no harm in dealing with it; otherwise, it is impermissible.