Hi @FRANCESCO DI CARLO ,
Do you mean you want to schedule Teams meeting between two different organizations?
In my experience, Microsoft Teams gives two different ways to make that happen. The first is external access, the second is the guest access. You can use both external access and guest access if you want. For more details about these two accesses, you can learn it from:
https://learn.microsoft.com/en-us/microsoftteams/communicate-with-users-from-other-organizations
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