Selection variant & is not allowed

What causes this issue?

You have called an unallowed selection variant.

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?

When calling the transportation info, the selection variant may only
have the values 'A' (order), 'L' (delivery) or 'T' (shipment).

Error message extract from SAP system. Copyright SAP SE.