You need the service URL for the AvaTax calculation service.
Avalara provides two API environments, Sandbox and Production. Customers can use the Sandbox environment to test their integration, and the Production environment to store their vital business data. To request a Sandbox account, please contact Avalara Support.
The latest Avalara service URLs can be found at AvaTax SSL Certificate Changes.
For users who have existing implementations of AvaTax built using REST 1.0, refer to Legacy REST API.