How do I use a single-use exemption in Document Management?

The key to matching a certificate created in AvaTax with your integration is passing the customerCode (which is required) and matching the customer id you pass in your createTransaction request to the way you set up the exemption in AvaTax. If the exemption is set up as a "Single-Use Exemption," AvaTax expects that you’ll also pass a matching Purchase Order number value that can be set on an Order or Invoice and passed in the purchaseOrderNo attribute of the createTransaction request.