[jakejohnson]

You can sign up for a free trial with TaxJar right away without calling a sales rep, no CC required. Sandbox API environment is included for all plans, but marketed toward Plus plans. Once you log in, generate prod / sandbox keys from the account page.

[mgkimsal]

Nope. I've logged in. Registered. I'm a paying customer, using it in production, and there's no visible way to generate a sandbox key, except 'go to plus'.

From their docs: https://developers.taxjar.com/api/reference/#sandbox-environ...

* Sandbox Environment

TaxJar provides a sandbox environment for automated testing and development on all TaxJar Plus plans. After generating a sandbox API token, point your API client to the sandbox environment...

There is no sandbox API available without 'plus'. Perhaps you had an earlier version and are grandfathered in?