Is anyone else having trouble attaching bills to invoices

Let me help you piece things together.  Are you using automated sales tax? 

If so, in the new QuickBooks Online format, the system overrides line items with the default VAT rate linked to the customer's profile, leading to mismatched or incorrect VAT calculations. 

To fix this, 

1. Go to your Customer list,
2. Select the customer, and click Edit.
3. Under the Additional info tab, uncheck Assign default tax code to prevent QBO from auto-applying global tax rules to every line.

Also, if a billable expense is adding the wrong VAT rate to your invoice, you may need to unlink the expense, add a custom line item manually, and select the correct tax code from the drop-down list. Just make sure your tax settings are mapped correctly for all your products and services.

For further guidance, check out this article: Enter billable expenses.

If you have any additional questions, please don’t hesitate to reach out. We're always here to assist you.