The reason why your Sales Tax Center is showing an error or not loading at all can be due to the piled-up QuickBooks cache and Intuit cookies in your web browser. Caches and cookies help to make your browsing experience seamless and trouble-free. However, they can pile up and cause the QB Online website to not function properly. To eliminate issues with your Sales Tax Center, clear QuickBooks cache and cookies from your web browser.

https://proadvisorsolutions.com/blog/quickbooks-online-sales-tax-center-not-working/