Symptoms
When trying to create a new Planner tab in Microsoft Teams, a team owner receives this error message from the Teams client:
'Failed to create the plan'.
Cause
The browser allows a few things in Planner that Teams doesn't. At least this and the ability to upload files to a task, vs just a link to sharepoint or a URL. But it doesn't matter where or how the Planner was created. Microsoft Planner lets you easily bring together teams, tasks, documents, and conversations for better results. Get more work done with Planner. Create Kanban boards using content-rich task cards with files, checklists, labels, and more. Collaborate in Planner and Microsoft Teams and check visual status charts—all in the Microsoft cloud.
The owner isn't a member of the Microsoft 365 group associated with the team. This prevents the Planner API from triggering the plan creation.
Resolution
Planner In Teams App
Add the owner as a member of the Microsoft 365 group. For more information, see Add or remove members from Microsoft 365 groups using the admin center.
More information
How To Create A Planner In Teams
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