We are unable to contact the source site

Hello,
I have all working fine, new WP installation, FTP access that is working, no firewall…
I got “We are unable to contact the source site. Due to this the migration cannot be completed.”. I tried many things but had no success. But what most bothers me is that it doesn’t tell me exactly is the cause of failure. I can only guess, waste my time, just shooting into the darkness. Searching here in the forum, when people ask the very same question, you look at your log and let them know what is the root cause. Why not make it easier?
So please, what failed in migration of https://elitevoyage.com/ ? Thank you