Take foreign exchange margin trading as an example. The selling price here is 1 17.47 and the buying price is 1 17.50. The price difference of 0.03 is what we call spread, that is, the transaction fee is three points.
If you do more now, the entry price is 1 17.50. When the purchase price reaches 1 17.53, your income is exactly 0, that is to say, you have just earned back the money of the spread fee, and then if the market continues to rise, you will start to make a profit.