Been trying to use the HTTP connector and graph with delegated API permissions to update the owner of a Plan.
According to the docs it looks to me like it should be possible:
https://docs.microsoft.com/en-us/graph/api/plannerplan-update?view=graph-rest-1.0&tabs=http
But I am getting the following error:
Schema validation has failed. Validation for field 'ContainerId', on entity 'Plan' has failed: This field is read only and cannot be changed.
The request looks as follows:

Running the same request as above but updating the 'title' instead of 'owner' works.
I am owner of both of the 365 groups, the current one and the one I am trying to move it to.