I appreciate you following the steps to switch from standard accounting to cash accounting in QuickBooks Online (QBO), burtonwallis. Let me add additional steps to change your VAT accounting scheme in QBO.
Since it's showing invoice dates in your Box 1 instead of amounts received, I recommend reviewing those transactions from April to June if they're already marked as paid. You can also double-check the VAT settings to ensure you have selected the Cash Account scheme. Once confirmed, you can generate the VAT return to verify if Box 1 is updated.
Then, run the VAT 100 report on the standard scheme from 01/01/2024 - 31/12/2023. Also, run the same report for the cash scheme with the same date periods. Once generated, check the difference between these reports.
When running the reports, ensure to change the accounting scheme if it's for standard or cash. Next, if the balance on the Open returns transactions matches the difference of the reports, it means it's correct.
However, if the open transactions don't match, the report picks up an invoice from an earlier date. If so, you can consider changing the start date to a much earlier date.
Refer to this article for more information about open transaction adjustments: Change the VAT accounting scheme in QBO.
In addition, refer to this article to learn how to adjust your VAT liability in QBO: Make VAT adjustments in QBO.
Comment on the post if you still have concerns about managing your tax settings in QBO. I'm always here to help you.