No unique selection: street or P.O. box.

What causes this issue?

For the address the application can specify whether to use the street
("S") or the P.O. box ("P"), but at runtime is passed the value &VAR1&
which is not valid.

System Response

Warning, the P.O. box has first priority.

How to fix this error?

Pass a valid value.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.