Either the size of the copied order is too large or you have already several open positions using margin and probably few P&L consequently decreasing the free margin your account had during a period of time, which leads to insufficient free margin to execute the copy on the slave. This is your broker that return us this "Insufficient margin/Failed Margin" error when trying to open the position.

Please close some open positions or add funds to your account, and try again to place an order.