Page transformation using PnP Modernization script not working (On-premises to SharePoint Online)

Hello,

We are migrating SharePoint 2016 on-premises to SharePoint Online. We are following below script for page transformation.

https://github.com/pnp/modernization/blob/dev/Scripts/PageTransformation/Convert-OnPremisesPublishingPages.ps1

We are able to connect SharePoint 2016, but it is throwing error as "The Remote Server returned an error (401) Unauthorized"

Please help if we are missing something.