Error Message:
The administrator must have a SharePoint Online license to perform the migration.
You need a SharePoint license because OneDrive is built on top of SharePoint.
Resolution:
In order to perform an administrative login and use the administrator rights, we need the administrator to have a SharePoint Online license.
If, after granting the license, you keep getting this error, retry the migration a bit later. Office 365 might take time to propagate the license everywhere.