Port '&' does not exist in the table of port descriptions

What causes this issue?

The file name of the outbound file is to be created for the port &v1&.
However, the port does not exist (any longer) in the table of port
definitions.

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?

Create this port or use a port which already exists.
IF &DEVICE&='SCREEN'
<DS:TRAN.WE21>Execute function</>
ENDIF

Error message extract from SAP system. Copyright SAP SE.