Fix WooCommerce Tax & Shipping

I run a U-S-based WooCommerce store from New Zealand and have run into two connected problems: no sales tax is showing at checkout and my flat-rate shipping fee disappears once a customer types in a U-S address.

The store currently relies on the “Tax Rate Upload Plugin by Adam Bowen,” yet I’m unsure whether the state-by-state rates were ever imported or mapped correctly. Core WooCommerce settings for taxes and shipping zones look fine at a glance, but not sure why I'm not getting tax and shipping issues.

What I need:
• Tax must calculate and display automatically for every U-S state and territory during cart and checkout.
• The existing flat-rate shipping option must appear consistently whenever a valid U-S address is entered.

thank you