We can't sign to Avalala's "STARTER" plan

Problem/Motivation

We are a web development company in Japan. We have been commissioned by a Japanese semiconductor manufacturer to build a semiconductor e-commerce website for their subsidiary located in California, USA. The sales of this semiconductor e-commerce website are extremely small because it is only used by circuit designers to purchase semiconductor components for prototyping purposes.

However, we had to calculate Sales Tax in order to sell to customers within the state of California. And we cannot allocate a large amount of expenses to that calculation.

We have chosen the "Drupal Commerce Connector for AvaTax." Because we can operate it for $50 per year.
https://www.avalara.com/us/en/products/integrations/drupal-commerce.html...

You can reach this page:

1. clicking on the banner at https://www.drupal.org/project/commerce_avatax →
2. clicking on "Pricing" link at https://www.avalara.com/us/en/products/integrations/drupal-commerce.html

We have completed the e-commerce website and contacted Avalara to inquire about purchasing a license.
However, Avalara's staff replied, "We are not aware of this page, and you cannot purchase at such a low price."

We can write inquiries using translation software, but we cannot speak in complex English conversations via phone. So I don't understand why Avalara has this attitude. Does anyone have any insights on this? Additionally, do you have any advice on how we should proceed? Could you please provide advice on how to proceed with negotiations?

I apologize for my poor English.