# Purchase order number

Source: https://developer.avalara.com/marketplace-integration-guide/transactions/certification-requirements/po-number/

**Endpoints/models used:** [CreateTransactionModel](https://developer.avalara.com/api-reference/avatax/rest/v2/models/CreateTransactionModel/)

Your integration should allow users to pull in the purchase order number that's associated with a transaction. This PO number is supplied at the header level using the `purchaseOrderNo` field.

A PO number provides the ability for a single-use exemption certificate to be applied to a particular customer. For example, when a PO number and customer code match a single-use certificate record, then an exemption will be applied.

[![Closed](https://avalara-devdocs-prod.mcoutput.com/avatax-for-marketplaces/Content/Skins/Default/Stylesheets/Images/transparent.gif)Example](javascript:void\(0\);)

```
{  "type": "SalesInvoice",  "companyCode": "DEFAULT",  "date": "2024-07-16",  "code": "MyDocumentCode",  "customerCode": "ABC",  "purchaseOrderNo": "123456789",  "commit": true,  "currencyCode": "USD",  "description": "Yarn",  ...,} 
```