Nexus Tax is when an internet sale is between two entities in different states or where delivery is in a different state than the home location of the selling entity.
Here is the explanation and WooCommerce solutions
This link woocommerce.com/posts/how-to-save-time-and-correctly-handle-woocommerce-accounting-and-invent
These are the people who are on top of this, but Stripe is poised to solve this pain point soon and push these people out of the major market share position.
This link https://www.avalara.com/eu/en/resources/tools/free-us-sales-tax-risk-assessment.html
New Zealand has a good explanation of Tax Nexus on this page https://my.nzte.govt.nz/collection/united-states-market-guide/article/understanding-tax-in-the-united-states