When doing a pre-migration check or copying a site object, one of the following messages is displayed:
When migrating site objects, it is strongly recommended to have 'Site Collection Administrator' permissions on your source site.
When migrating site objects, it is strongly recommended to have 'Site Collection Administrator' permissions on your destination site.
We highly recommend that the user used for a structure migration possess the site collection administration rights on the source and the destination sites. Those permissions are required to read all the required information from the source and to update the destination environment accordingly.
Grant site collection administrator permissions to the user performing the migration both at the source and at the destination. For more information on granting permissions, see Administrative permissions.
Note: To add site collection administrator permissions using PowerShell, see Add site collection administrator.