How To Fix VP450 - Partner function & not defined at header level

VP450 - Overview

• Message type: E = Error

• Message class: VP - Vertriebsbelegpartner

• Message number: 450

• Message text: Partner function & not defined at header level

What causes this issue?

The <GL:partner_function>partner function</> &V1& is defined as item
partner function in <GL:Customizing>Customizing</> and therefore does
not exist in the document at header level.

Error message extract from SAP system. Copyright SAP SE.

VP450 - Details

• The SAP error message:
  VP450 Partner function & not defined at header level
  typically occurs in Sales and Distribution (SD) module when processing sales documents (like sales orders, deliveries, billing documents), and it indicates that a required partner function is missing or not maintained at the header level of the document.
  
  Cause
  
  The partner function (e.g., Sold-to party, Ship-to party, Payer, Bill-to party) that is mandatory for the sales document type or process is not assigned or maintained at the header level of the sales document.
  The system expects this partner function to be present because it is defined as mandatory in the partner determination procedure for the sales document type.
  This can happen if:
  The partner function was accidentally deleted or not entered.
  The partner determination procedure is incorrectly configured.
  The sales document type requires a partner function that is not maintained in the master data or document.
  Customization or user exit logic removed or failed to add the