S4HANA Billing Document Output Management -> IDOC?

Hello everyone

Tried to set up BRF+ etc for Billing Document Management as discribed in blog

https://blogs.sap.com/2016/04/01/output-management-via-brf/#respond...

whenever I try to send an output from invoice i get the same error:

"No entry for partner function '' in table TPAR".. (equal error as in this blog/comment)
PartnerAgreements etc are all done... does anyone has an Idea what is missing