Hi,
if you want to add an invoice, please use the Documents object.
At the moment you're trying to add an invoice (object id 13) but you're using the xml format of a Business partner.
Please run the metadata retrieval and check the object structure under HELP -> B1 object.
Best regards
Bastian
P.S..:
B1 object atom automatically creates a template of the selected object in the predecessor xform, when pressing "Generate Schema".