# Purchase order number

Source: https://developer.avalara.com/avatax-for-ap/uao6796860045692/

# Purchase order number

**Element type:** Required

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

Your integration must 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.

**View example**:

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