Check the source and target AD environments, and ensure your firewall is not blocking our Directory Sync agent or the following ports:
Connecting to the Directory Sync web interface uses TCP port 443 (HTTPS).
Agent connections are initiated by the agent and require port 443 access to Directory Sync SaaS application.
Connecting to DCs uses TCP on ports 139, 389 (UDP), 445, and 3268.
Copying SID History uses TCP on ports 135, 137-139, 389 (UDP), 445, 1027, 3268, and 49152-65535.
For further details click this link to our online documentation:
https://support.quest.com/on-demand-migration/kb/4346298/which-ports-are-required-by-the-odmad-directory-synchronization-agent-4346298