Relationship type does not fit the partner function category

What causes this issue?

The specified relationship type does not correspond with the partner
function category.

System Response

Many partnter function categories are hard coded in order to correspond
with a particular relationship type. For example, the partner function
category 'sold-to party' corresponds with the relationship type 'is /
has the sold-to party'.
The partner function category 'undefined partner' can, however,
correspond with every relationship type.

How to fix this error?

Either delete this relationship type or enter the partner function
category 'undefined partner'.
If you delete this relationship type. the system automatically uses the
relationship type that corresponds with the partner function category
you have entered.
Use the 'undefined partner' primarily when no other partner function
category meets your requirements.

Procedure for System Administrators

To define relationship types and to display a list of them in
Customizing, choose Cross-Application Components -> SAP Business Partner
-> Business Partner Relationships -> Basic Settings -> Define
Relationship Types.

Error message extract from SAP system. Copyright SAP SE.