When doing a pre-migration check or while performing a migration, the following message is displayed:
When using the Insane Mode, it is necessary to have the site collection administrator permissions at your destination.
We require that the user used for a migration using the Insane Mode possesses the site collection administration rights on the destination site. Office365 will return an error if the user is not the Site Collection administrator of the destination site collection, since you need to have this permission to create a migration job.
Note: To add site collection administrator permissions using PowerShell, see Add site collection administrator.