Need Help with BAPI_PO_CREATE1

I can execute BAPI_PO_CREATE1 successfully in SE37 and create a Purchase Order.

However when calling the BAPI remotely, I get these messages:

• No instance of object type Purchase Order has been created. External reference:
• PO Header Data still faulty
• No master record exists for vendor 20220
• The material 3000223 does not exist or is not activated
• Can delivery be met?
• Source not included in list despite source list requirement

In the PO Header, I am supplying:

• COMP_CODE
• DOC_TYPE
• VENDOR
• PURCH_ORG
• PUR_GROUP
• CURRENCY

In the PO Line Item, I am supplying

• PO_ITEM
• MATERIAL
• PLANT
• QUANTITY
• PO_UNIT
• AGREEMENT
• AGMT_ITEM