I appreciate your initiative in troubleshooting the error with your VAT registration, @corrinats. Let me share some possible reasons for this and provide guidance in resolving the error effectively.

To better assist you, I would like to clarify the exact error message you've encountered. This information is essential for us to identify the root cause and provide a tailored resolution to the problem you're facing.

If QuickBooks Online (QBO) isn't accepting your new VAT number, it could be due to several reasons: incorrect input, issues with your tax settings, or a mismatch between the VAT registration number in the VAT Centre and HMRC's records.

In this case, it's important to double-check the number for accuracy, verify your company's tax settings, and ensure that the details in QBO are correct, whether you are authorizing for your business or on behalf of a client. Additionally, confirm that you’re using MTD-specific credentials rather than general Government Gateway credentials.

If the issue persists, I recommend contacting our QuickBooks Online Support  team. They are equipped with specialized tools, including screen-sharing capabilities, which allow them to take a deeper look at what's causing the error, and guide you to get past it.

1. Sign in to your QBO company, select (?) Help.
2. Click the Search tab and enter a keyword to your concern.
3. Select Contact Us.
4. Choose to Callback to Chat to connect with us.

Furthermore, you can visit this article that explains how to adjust your VAT liability, what happens after you make a VAT adjustment, and things to remember before submitting a VAT return: Make VAT adjustments in QuickBooks Online.

Feel free to Reply to this thread whenever you have additional questions about VAT and using the MTD function. The Community is here to help anytime.