Tax was not successfully calculated the first time the bill run triggered a calculation in Zuora.
Re-run the bill run through the connector's manual bill run page.
Note: Manual bill run page can be found in Z-Billing Settings, go to the Setup Profiles, Notification and Email Templates section.
Then go down to Bill Run Completion | Completed Status and click on [Edit].
Highlight everything in the URL callout field. One way to do this is to click your cursor to the left side of https... and then while holding down shift press the End key. Copy this long string.
Paste the string into your web browser to bring up the manual bill run page.