Several delivery notes in one IDoc

What causes this issue?

The IDoc with the bill of lading &V1& contains several delivery notes.
The first of these has the number &V2&.
The processing of an IDoc with several delivery notes is currently not
possible.

How to fix this error?

Get the supplier to ensure that only IDocs with just one delivery note
are transmitted.

Error message extract from SAP system. Copyright SAP SE.