There could be two reasons for receiving this message:
1. Insufficient cash
If you receive the message "You have insufficient cash in the account to make this trade", please make sure you have enough cash on your account to place the trade by comparing Cash balance available and a Nominal value of position in a trade ticket.
2. Pending Buy orders
Another reason for rejection is pending Buy orders.
When placing a Buy order, the system checks the Cash balance available plus Cash reserved for pending Buy order / orders execution.
Please cancel the pending Buy order / orders and try to place your trade again.