Welcome back to the Community, @cmacp. I know what transactions appear in the Tax Details report in QuickBooks Self-Employed (QBSE).
Transactions available on the aforementioned report are business income, other business income, business expenses; and either allowable or disallowable. Since you mentioned that the transaction you had categorized to other business income isn’t showing on your Tax Details report, this could be due to its categorization.
To rectify this, you’ll want to locate these transactions and double-check to what category it has been added. Once you have verified that it’s not in the category you want it to be, please consider re-categorising this transaction.
If you’re unsure of what category this should be added to, you can contact our Customer Care Team or reach out to your accountant for further guidelines. It is also to ensure that they are added to the correct line of your category.
I have added a guide for you in case you plan to handle your self-assessment taxes on your own in the future as a self-employed individual. Self Assessment for Income Tax checklist for QuickBooks Self-Employed.
Should there be anything else related to your Self-Employed reports or any other matter, feel free to provide the necessary details in your response. I am always ready and willing to assist you in any way possible.