What VAT rate to use to record sub-contract sales in Ireland in a way that properly records RTD details?

Hello there, @jhogan4.

To know the exact tax rate to use in recording sub-contract sales in Ireland, I recommend contacting your tax agency or an accountant for an advise. QuickBooks only depends on how you set up taxes. If you don't have one, you can click this link to find an accountant near you: Find an accountant.

For future reference, you can read this article to guide you in running a report for Return of Trading Details (RTD): Run a Return of Trading Details (RTD) report.

Let me know if you have questions about setting up sales taxes in QuickBooks Online. I'm always here to help. Have a great day.

It's up to QBO to set these up, it's not up to your accountant.  There is no VAT Code set up for Postponed Accounting either.