"Insufficient privileges to complete the operation" when listing Planner tasks from Project

Hi, it's only my time posting here, please let me know if I should be doing something differently!

I've searched throughout the internet and couldn't find a solution for this.

I've got a user running into a problem where the `/me/planner/tasks`, `/planner/buckets/{bucketId}/tasks`, and `/planner/plans/{planId}/tasks` endpoints return a `Authorization_RequestDenied` error. Here's an example response:

{
  "code": "Authorization_RequestDenied",
  "message": "Insufficient privileges to complete the operation.",
  "innerError": {
    "date": "2025-07-23T08:15:50",
    "request-id": "bd5f7056-a41d-439c-a0d7-d768cd82d1ea",
    "client-request-id": "362f376c-863e-0616-86f7-22c7c07c1352"
  }
}

While this happens for almost all of their groups and plans, it doesn't happen for one. The main difference between that which works and the other ones which don't is that all the ones that don't work were created in Microsoft Project (Platinum, I think?). The one that does was created in Planner.

We can, however, list the proper plans and buckets, just not fetch the tasks.

Is there any way around this? Is there some kind of special scope I should be asking for so the API calls work? Should I use the To Do API in some special way for this, instead?

Thank you so much!