Message type: E = Error
Message class:  CNV_DMC_SIN - Messages for s-innovations migration 
Message number: 455
Message text: ItemNo &1: Plant &2 is not assigned to company code &3
You have entered plant data which is not assigned to the corresponding
company code provided on sheet ' Material Document Header'.
The system issues an error message and will not allow you to continue with this transaction until the error is resolved.
Split the data according to Plants assigned to your provided Company
Code.
Error message extract from SAP system. Copyright SAP SE.
The SAP error message CNV_DMC_SIN455 indicates that there is an issue with the assignment of a plant to a company code during a data migration or conversion process. Specifically, it means that the specified plant (identified by &2) is not assigned to the specified company code (identified by &3). The item number &1 refers to the specific item in the migration process that is causing the error.
Cause: Missing Assignment: The plant is not assigned to the company code in the SAP system. This can happen if the plant was created but not linked to the company code. Incorrect Data: The data being migrated may contain incorrect or outdated information regarding plant and company code assignments.
Configuration Issues: There may be configuration issues in the system that prevent the proper assignment of plants to company codes.
Solution: Check Plant Assignment: Go to the SAP transaction code OX18 (or SPRO -> Enterprise Structure -> Assignment -> Logistics General
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