It is not possible to copy data from field 'Returns with shipping proc.'

What causes this issue?

You wanted to maintain the indicator (LFM1-KZRET) by coping data or
distributing vendor master data. This indicator determines whether
vendor returns are to be carried out with shipping processing.
This automatic creation of customer data is not supported in data
copying or during ALE distribution.

System Response

If the indicator is set, the system checks whether a customer
containing all the necessary sales areas has been created for the
vendor.

How to fix this error?

You have the following options:
You do not transfer this indicator, but enter it manually.
You first transfer the assigned customer, and then transfer the vendor
data.

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.