Please see the docs here- https://developer.intuit.com/docs/95_legacy/qbd_v3/qbd_v3_reference/030_entity_services_reference/purchase Billable status is applicable only when there is CustomerRef passed in the request and applicable to the specific account types: 1. Expense 2. Other Expense 3. Cost of Goods Sold
Please check if your Account types match the above.