This error means that Magic Keys tries to open an invalid order amount for this instrument. This happens because some non-currency instruments do not have micro or mini lot sizes.
Check your instrument specification (Ctrl-M, [right-click] -> Specification) and see "Min/Max volume" and "Volume step" parameters. MK's automatically calculated position size does not fit these. For example, MK tries to open 1.5 lots when Volume step is 1.0. You won't be able to manually open such position size either.
Check if your broker has duplicate instruments to remedy this, for example Axi broker: US500, US30, USTECH have volume step 1.0 lot, but S&P.fs, DJ30.fs and NAS100.fs have volume step 0.01 lots.
Could we add this to a feature request for MK: "Position size calculator to account for Min/Max Volume and Volume step properties of the instrument"?
