I think you need to read FAQ before you start to trade in Bitmex. After that, you need to watch a video about trading in Bitmex which is available on Youtube. There are so many good videos you can watch to learn how to place an order, and I think your problem is about setting the right number in the column.
This video is an example for you can learn:
Placing Orders, Setting Stop losses and Targets, Leverage and MarginBitmex Stop Loss Tutorial And Fees ExplanationI am sure there is many more good video for you to watch, you can get something from the video. I hope you can solve the problem, so you don't have a problem to trade in Bitmex.
You give the right advice. Topic starter need to start with their implementation. If this does not help to solve the problem, then he can read reviews on various resources. Reviews, necessarily dedicated to this exchange. As examples:
https://www.trustpilot.com/review/bitmex.com or
https://revain.org/exchanges/bitmex. If the above does not help, then there is nothing left but to change the exchange.