I invited someone to the Microsoft to-do list, but they cannot sign up.

Hi @Sinclair Ada

I recently came across the same issue reported by another user in the Microsoft To Do community. However, I cannot reproduce the issue at the moment.

First, please try the troubleshooting steps I mentioned in this thread: I invited a Microsoft to-do list, but the other party couldn't join - Microsoft Q&A

There was also a Microsoft To Do incident related to users being unable to join shared lists in January 2026: TO DO app: can't join list - Microsoft Q&A. Because of that previous incident, I checked the current Service Health in the Microsoft 365 admin center. However, I don't currently see any related incident reported there.

If you try the steps above and the issue still occurs, I recommend checking with your IT administrator to see whether other users in your organization are experiencing the same issue.

If you're unsure who your IT administrator is, please refer to How do I find my Microsoft 365 admin? - Microsoft Support 

Although there has been no update confirming whether the issue was resolved in the thread I mentioned above, similar reports appear to be coming from multiple tenants, I recommend that your IT administrator raise a support ticket through the Microsoft 365 admin center so Microsoft can investigate the issue further from the service/tenant side.

I hope this helps.

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