Market-on-Close (MOC) orders are supported on the LSEETF exchange, but only if you direct your order to LSEETF instead of SMART. To direct your order to LSEETF in TWS, click on "SMART" and change it to "LSEETF".
Please note, this order type may only be supported in your live trading account and not in your paper trading account.
More information on how to create an order in TWS can be found in our Users' Guide.