Migration account does not have permission to perform this operation. Check if admin@______.onmicrosoft.com has been added to user site collection

Issue

When migrating, from or into, Office 365 this error may be thrown out when using the "Check Connections" feature, or whilst running a migration for a specific user.

Reason

A global administrator isn't being used within the configuration or the insufficient permissions have been configured. Another reason could be that the administration account hasn't been added to the user's site collection.

Fix

Add the user as a site collection administrator:

• Go to your SharePoint admin centre (https://yourdomain-admin.sharepoint.com) and login with an admin account.
• Click on 'user profiles' in the left hand menu and then 'Manage User Profiles'
• Look for the effected user (example@yourdomain.com) in the 'Find Profiles' and click 'Find'
• Click on the user, this should bring up a menu with 4 options. Click on 'Manage site collection owners'
• Enter example@yourdomain.com into 'Site Collection Administrators' and click on the icon that looks like a user with a tick (highlighted in red in the attached) this will check the name exists.
  Click 'OK'