Error in billing item &1/&2: customer number is initial

What causes this issue?

No material number could be determined for the recycling declaration
from billing item &V2& for document &V1&.

System Response

The system can not carry out calculation of the splitting factor for
regional processing for this billing item. The item was neverless
valuated with a proportion of 100%.

How to fix this error?

Please check the billing item &V1& / &V2& and, if relevant, the setting
in general REA Customizing for "Customer number table and field" in the
section "Control of Declaration/Origin Movement Data".

Error message extract from SAP system. Copyright SAP SE.