The ideal is to be checking the promotions of pairs that do not charge a commission.

Hello, good evening, can someone help me with this question? I bought bitcoin, let it rise a bit, and then withdrew the money. It arrived in my wallet, but once the bitcoin dropped, I bought again with the aim of making some dollars (approximately 15). However, when I bought, I noticed that the money was less, meaning that according to the purchase I would earn 15 dollars. I had 1100 when I withdrew, but when I bought when the bitcoin was lower, I only got 1085. In other words, I lost 16 dollars even though the estimated amount was profit. Can someone explain this to me or where can I find the instructions? Thank you.