Customer & is not defined for function & (table TPAKD)

What causes this issue?

The account group of the current customer is not defined for the
required partner usage.

How to fix this error?

Within customizing, select Sales and Distribution -> Basic functions ->
Partner determination -> Define partner functions -> Customer master
data -> Environment -> Acct grp assignment. Here you assign the
function required to the current account group.

Error message extract from SAP system. Copyright SAP SE.