How To Fix VP444 - Function & is defined in the header and not deletable here

VP444 - Overview

• Message type: E = Error

• Message class: VP - Vertriebsbelegpartner

• Message number: 444

• Message text: Function & is defined in the header and not deletable here

What causes this issue?

Header partners cannot be deleted at item level.
INCLUDE 'NA_NO_PROCESSING_1' OBJECT DOKU ID TX LANGUAGE D

How to fix this error?

Delete the partner at header level.
If the <GL:partner function>partner function</> &V1& in
<GL:Customizing>Customizing</> is not defined as a compulsory function
for the document header and is marked as alterable, it can be deleted at
header level. The entries present at item level in this partner
function are then automatically deleted.

Error message extract from SAP system. Copyright SAP SE.

VP444 - Details

• SAP Error Message:
  VP444 - Function & is defined in the header and not deletable here
  
  
  Cause:
  This error occurs when you try to delete or change a function (e.g., a task, operation, or activity) in a sublevel or item level of a document or structure, but the function is originally defined and controlled at the header level. SAP does not allow deletion or modification of such functions at lower levels because the header-level definition governs them.
  In other words, the function you are trying to delete or modify is maintained at the header (top) level of the document or structure, and the system restricts changes at subordinate levels to maintain data consistency and integrity.
  
  When does this typically happen?
  
  In Project System (PS), when working with networks or WBS elements.
  In Sales and Distribution (SD) or Production Planning (PP) when dealing with functions or operations linked to header data.
  When trying to delete a function in a