You’re unable to withdraw the full ‘Balance Available’ because some of that amount may be

• Pending Settlement:

After selling stocks, you’re free to trade with your available amount immediately; however, you cannot withdraw on the same day. T+1 or T+2 days later (depending on the segment), you’ll be able to withdraw.

• Margin Utilized:

If the money is pledged or used as margin (for your open positions), it cannot be withdrawn.