# How do I use a single-use exemption in Exemption Certificate Management (ECM)?

Source: https://developer.avalara.com/products/ecm/integration-guides/document-management/mgd7792342619074/

Guide: Exemption Certificate Management (ECM)

# How do I use a single-use exemption in Exemption Certificate Management (ECM)?

Learn how to use a single-use exemption in ECM.

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.