In MultiCharts one is able to trade on a spread only if it is exchange traded spread and it is provided by your data vendor as a single separate instrument that is added to QuoteManager database (see [https://www.multicharts.com/trading-software/index.php?title=Operating_Symbol_List#Adding_Symbol_from_Data_Vendor_Supplied_List Adding Symbols to Database]) and mapped correctly to the corresponding broker instrument in [[Symbol Mapping]] window. If there is no such instrument on data source end and at your broker, then it is not possible to trade such spread.