Questrade how to buy stocks in USD

This one may be very specific, but I tried for a couple months to buy stocks on the NASDAQ without success, gave up and bought ones on the TSX.

For example if my account says Available Balance: $1,000 CAD, $0 USD… and my order costs me $600 USD, it will show ‘Available Balance: $0, Cost: $600, New Balance -$600 USD’ and blocks the transaction. Do I need to trade that $1,000 CAD on the FX to USD myself? Doesn’t sound very convenient.

Thanks!