To enable users to add guests within the tenant
Sometimes you need users to add guests on their own. Normally, this can only be done by Admins. To enable this:
- Log into the Office 365 admin portal (https://admin.microsoft.com/)
- Go to Settings | Org settings (left blade) | Security and Privacy (menu bar) | Sharing
- Check Let users add new guests
To add a new guest user
In the Office 365 admin portal:
- Select Users | Guest users
- Click + Add a guest user. You’ll be redirected to Azure
- Select Invite user and enter their details.
The guest user needs to accept the invite before gaining access to anything.
To add them to a Planner board, follow https://support.microsoft.com/en-us/office/guest-access-in-microsoft-planner-cc5d7f96-dced-4da4-ab62-08c72d9759c6