Clients who are unable to trade more than one futures contract per order should first check their order presets to ensure that they have not established an order size limit in the precautionary settings.  If this is not the case,  then the restriction has likely been imposed by IBKR due to the client's failure to accept the Arbitration Agreement which automatically imposes a trading limit of one contract per order.  Clients decline to accept the agreement when presented through the application process but who subsequently wish to accept need to login to Client Portal and execute the Arbitration Agreement.