Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Dear Alexandru,
Good day! Thank you for posting in Microsoft Community. We are happy to help you.
From your description, it seems that all users in your organization cannot access Planner and encountered an error message.
If my understanding is right, we have also tested it on our side and we cannot reproduce the same situation as yours.
And we have also checked it on our side and we didn’t receive the report of such issue.
Given this situation, we do understand the inconvenience caused by it. Since we cannot reproduce the same situation as yours and entire tenant has the same problem, we assumed this issue may be related to you tenant and may need to be checked from background. The best way to troubleshoot the issue is to report the issue to the related Team. We’d suggest you contact your office 365 administrator to go to Office 365 Admin Center-> Support-> New Service Request, the support engineers there have the correct escalation channel and this is the most efficient way to report such issue. You can refer to this article to check the way how to raise a ticket. Ways to contact support for business products - Admin help.
If the scenario above is not consistent with yours, you can also post back and point that.
We look forward to your reply. Thanks for your cooperation.
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Sincerely,
Sukie | Microsoft Community Moderator