What causes this issue?

A shipment could not be generated due to the specified capacity
criteria. There are several reasons for this:
Each delivery has a certain weight or volume that exceeds the shipment
capacity.
The shipments created were so small that they have not met the
specified minimal criteria (minimum weight, minimum volume or minimum
number of deliveries per shipment). Therefore, the shipment was not
created.

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?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.