No mode-of-transport category found for delivery &1

What causes this issue?

To select the valid dangerous goods data, you must determine the mode
of transport category/ies for the dangerous goods transport. However,
no mode of transport category could be found for delivery &V1&.This
could be due to the fact that the route has not been allocated a
shipping type and thus a mode of transport category.

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?

Check if the delivery route has been allocated a shipping type.

Error message extract from SAP system. Copyright SAP SE.