Shipping type & does not match shipping type & for route &

What causes this issue?

The shipping type of the item does not match the shipping type that is
assigned to the route.

System Response

Entry of route not allowed.

How to fix this error?

Enter a shipping type that is the same as the shipping type of the
route. The shipping types must be the same so that the deliveries can
be selected for the shipment.

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.