ConvertTo-SPOMigrationTargetedPackage: The remote server returned an error 401 unauthorized

I'm following this article to upload data to Sharepoint Online

https://technet.microsoft.com/en-us/library/mt210445.aspx#BKMK_NetworkUpload

I've made it through every step until ConvertTo-SPOMigrationTargetedPackage where it returns

ConvertTo-SPOMigrationTargetedPackage: The remote server returned an error: (401) Unauthorized.

I've already authenticated with Connect-SPOService, why is it throwing this error?