Answer
When generating a Direct Entry (ABA) file, the final step of the wizard includes an Include Debit Entry? checkbox. This adds a balancing debit record to the ABA file alongside the individual payment credit records.
Most banks do not require this, but some financial institutions will reject an ABA file that does not contain a matching debit entry. If your bank returns an error when you upload the file, regenerate the ABA file with this option enabled.
Desktop App
On the Save File step of the Direct Entry wizard, tick Include debit entry (i.e. balancing entry)? before saving the file. The setting is remembered for your company, so future files will include the debit entry automatically unless you uncheck it.
Online App
On the Save Direct Entry File step of the Direct Entry wizard, tick Include Debit Entry? before clicking Download Direct Entry File. The same checkbox is available when generating a Direct Entry file for superannuation payments, and also on the regenerate ABA tool.

For a full guide to creating Direct Entry files, see How Do I Make Payments Using a Direct Entry Banking File?