By default the withdrawals function is disabled on sub-accounts. You can enable withdrawals for your sub-accounts by clicking the settings button in the row corresponding to the sub-account chosen.
You can also do this by selecting several sub-accounts at once.
To restrict withdrawals for a certain sub-account, just choose the account and click the "Disable" button. Freezing the sub-account stops all its activity. Both these options can be cancelled at any time in the same tab.
Important: trading volumes of all sub accounts and your master account are summed. The fee tier is calculated based on the total volume of sub and master accounts.