You could have missed this passage, if you went for the Azure Active Directory Sync Tool on your own, instead of following the small wizard on the Microsoft Intune account page.
While running the Configuration Wizard of the Azure Active Directory Sync Tool, you may get the error:
An error occurred. Error Code: 15. Error Description: Directory Synchronization is not yet activated for this company. To activate Directory Synchronisationm click the Active button on the Directory Synchronization page in your Admin Portal
Directory Synchronization is not yet activated for this company
No worries; here’s how to enable
Log on to: https://account.manage.microsoft.com/
Navigate to Management – Users. Click Single Sign-on: Set up
Set Up AD Sync Intune
Then click Active at step 3.
Set Up AD Sync Intune
Again, click Activate to confirm.
Done, You should now be able to finish the Configuration Wizard of the AAD Sync tool