When using OFX direct debit, you can choose to deposit funds into your account for general use at any time, or you can deposit only the necessary amount for a specific payment during the payment flow.

To do a general deposit, click on "Add funds" on the Dashboard to open the funding options, click on Direct Debit, and select the linked bank account you would like to draw funds from.

 

Once you've selected your account, enter the amount you'd like to draw from your account and deposit into OFX, and select the date you want the funds to arrive.

 
Once you set your chosen amount and date, click "Fund account" to instruct the direct debit. Once it's confirmed, you can track the progress via the "Direct debit activity" tab.

To fund a specific payment amount, select the account you'd like to draw funds from the "Direct debit from an external bank account" section in the drop down labeled "Funding method" on the payment form. This will automatically instruct a direct debit for the right date and amount for your payment once it's confirmed.