If you encounter an issue while you copy pre-existing data between D365 FO and Dataverse, an initial sync error is given: “Copying pre-existing data completed with Errors. For additional details, go to Initial sync details tab”.

Investigate the error and choose how to solve it:

• Fix the underlying issue. When the issue is fixed, re-run the execution.
• It is not required to synchronize the records with errors. In this case, re-run the execution without errors.

For more information, refer to: Error management and alert notifications.