# Purchase Order number

Source: https://developer.avalara.com/avatax-dm-combined-erp/sales-tax-badge/transactions/cert-po-number/

# Purchase Order number

**Element type: Suggested**

**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 is associated with a transaction. This PO number is supplied at the header level.

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.

```
{    "lines": [        {            "number": "1",            "quantity": 1,            "amount": 100,            "taxCode": "PS081282",            "itemCode": "Y0001",            "description": "Yarn"        }    ],    "addresses": {        "singleLocation": {            "line1": "2000 Main Street",            "city": "Irvine",            "region": "CA",            "country": "US",            "postalCode": "92614"        }    },    "type": "SalesInvoice",    "companyCode": "DEFAULT",    "date": "2020-10-16",    "code": "XYZ",    "customerCode": "ABC",    "purchaseOrderNo": "123456789",    "commit": true,    "currencyCode": "USD",    "description": "Yarn"}
```

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