When will we able to test Pro Tax with accounting periods ending after 31 March 2023?

It's nice to see you again in the Community forum, @richard96. I'll be glad to help share insights about using the Pro Tax in QuickBooks.

 Since you already submitted the CT600s except for one, I'd suggest contacting our Customer Support Team. They can provide the exact date when you can use the Pro Tax for years ending April 30, 2023, and later. They can also provide updates about tax calculations and filings.

To reach them, follow the steps below:

1. Sign in to your QuickBooks Online company.
2. Select Help (?).
3. In QB Assistant, enter the topic you need help with. You can also enter questions.
4. In Search, click Contact Us to connect with a live support agent.
5. Choose a way to connect with us:

• Start a chat with a support expert. Live chat all day, M-F.
• Call us. M-F, 8:00 AM to 10:00 PM, and S-S, 8:00 AM to 6:00 PM.
  

 For complete details, see this article: QuickBooks Online Support. It also contains a video tutorial for visual reference.

• Prepare your annual accounts using Workpapers in QuickBooks Online Accountant
• File your Corporation Tax return using Workpapers in QuickBooks Online Accountant

If there's anything else that I can help you with, please let me know in the comment section below. I'll be always around ready to help.