Ship-to party &1 is not assigned to a sold-to party

What causes this issue?

When determining the sold-to party for a ship-to party, no
ship-to party->sold-to party assignment could be found.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

In the partner function screen of a sold-to party master record for
the current sales area, enter the ship-to party under the function
'ship-to party' ein.

Error message extract from SAP system. Copyright SAP SE.