Hello there, @Shanjenks.
I'm here to help check why your tax payment are showing as zero and help share some information about employed and self-employed income.
Transactions on your account must be self-employed business income and expense related only. In this case, your employed income must not be added to your self-employed income. You can add/set up your employed income under your tax profile which helps determine what tax bracket do you belong. For additional reference, you may check this article: QuickBooks Self-Employed UK Tax Profile Set Up.
On the other hand, to check why your estimated tax payment is showing as zero and to learn more about how QuickBooks calculate your tax payments, you can also check this article: How QuickBooks Self-Employed calculates tax payments.
If you need further assistance checking your taxes securely, you may get in touch with our QuickBooks Self-Employed Support.
As always, please don't hesitate to add a comment below if you have any other taxes concerns. I'll be always here to help you.
