When connecting to ShareGate Overcast, you may need to specify your tenant ID.
You can find this value two ways.
Through the website
If your Azure AD is associated to a domain, you can go to https://www.whatismytenantid.com and enter your domain name. Your tenant ID will then be displayed.
Through the Azure Portal
The typical way to recover the ID is through the Azure portal.
Click on Azure Active Directory then click on "Properties". Your directory ID will be displayed at the bottom (which doubles as your tenant ID).