Publishing failed. Intransit Plant of shipment &1 was not maintained

What causes this issue?

Intransit plant was not entered.

System Response

System could not publish shipment due to the missing intransit plant.

How to fix this error?

Enter an intransit plant for the relevant shipment in the TSW Data
section of the Shipment Details tab.

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.