Unfortunately, due to the way that NinjaTrader 8 processes data and order information, we advise that you do not use Chart Trader to place orders to MGC with your Rithmic-based connection. You must use a different order entry window to place orders to MGC. This unexpected Chart Trader behavior is exclusive to the instruments MGC, HO, and RB and is a limitation that must be worked around.
Additionally, please follow the steps below to configure the exchanges for your MGC instrument;
Go to Control Center > Tools > Instruments
Select it with a single left-click
Select the field next to 'Exchanges' with a left click
Select 'Nymex' from the list (leave Globex selected as well)
Select Apply and OK
A video of this process is available HERE
Next, you will want to make sure that you are selecting the MGC 12-20 Nymex by adding it to an instrument list and designating an exchange by editing with the steps below;
Go to Control Center > Tools > Instrument List
Select your instrument list from the 'Lists' section on the left side
Type MGC and double click to add it to the list
Locate 'MGC 12-20' in the 'Instruments' section and select it with a left click
A video of this process CAN BE FOUND HERE
Once you have added the instrument to your instrument list, you may open that instrument in a Basic Entry, SuperDOM, or Order Ticket window from the Instrument drop down.
A video demonstrating this can be found HERE