This rather crude script successfully migrated 99.9% of our Plans, Buckets and Tasks from one MS Online tenant to another.

It has some pre-requisites in order to work: You must have all users and groups synced already, we had other native Powershell scripts to do this. You must have a service account user present in every unified group that has a plan, the script will run as this user. You need to register your application in Azure AD and set up ClientID key and Client secrets. You will need a bunch of delegated permissions for this app:

• Group.Read.All
• Group.ReadWrite.All
• Tasks.Read
• Tasks.Read.Shared
• Tasks.ReadWrite
• Tasks.ReadWrite.Shared
• User.Read
• User.ReadBasic.All

I set the same permissions in both tenants but you may want it slightly more restricted in the source.

This script works but was hacked together with a time frame in mind, there is most definitely room for improvement. More functions could be implemented and the ones that are there could be made more generic. It is what I like to call "just enough script to get the job done". We only needed to run this script once so I approached the point of diminishing returns rapidly. Although it should run fine to do an incremental after the initial run so I will probably run it again. Submissions for improvements would definitely be welcome.

The one and only time I ran it there were a couple of errors thrown up in the buckets and tasks sections that I think were to do with malformed JSON payloads. If I can figure out which ones failed then I will attempt to diagnose more and get into it.

I did also observe a condition whereby a plan could have more than one ID which threw earlier versions of the script off. I have corrected for this now and I suspect that the bucket and tasks issues described above were also down to this.

As always it should be run entirely at your own risk, I would definitely recommend a thorough audit before letting it loose against you production environment.

This script builds upon the immensely helpful stuff I gleaned from here: https://www.thelazyadministrator.com/2019/07/22/connect-and-navigate-the-microsoft-graph-api-with-powershell/