Hi NIKOLAOS,
Sorry to hear that you're experiencing this issue!
I am Bhavik, an Independent Advisor and a Microsoft user like you. Please note, I am not a Microsoft employee and don’t have direct access to your account, but I will do everything I can to help you with your queries. :)
Follow the steps mentioned below:
- Sign-in on Microsoft 365 Admin Center.
- Go to Groups and Shared Mailboxes
- In the Details pane, next to Members, click on Edit.
- Click on Add members and add the member you wish to.
Let me know in case of any further help is required.
Thanks
Bhavik
An Independent Advisor