Creating Supplier Invoice Without Purchase Order via Maintain Supplier Invoice

Dear Experts,

I am creating a Supplier Invoice using Maintain Supplier Invoice API in the Service Explorer , I set the DataEntryProcessingStatusCode to 2 so that the documents I posted will be just saved as draft, but upon posting it returns an exception that the Item does not reference to purchase order. How can create Supplier Invoice Without Purchase Order using the Same API , I had been reading the documentation but no luck it getting rid of the reference exception error.