Hi,
Please find my site settings below:
1) Authentication/Registration/Enabled - true
2) Authentication/Registration/OpenRegistrationEnabled - false
3) Authentication/Registration/AzureADLoginEnabled - true
4) Authentication/Registration/InvitationEnabled - true
Now, when I sign-in using Azure AD. it is asking me for invitation code.
I don't know why it is asking for Invitation Code. Because I'm signin using Internal User.