Connection to ‘mywebsite.ca/wp-admin’

Hi everyone,

I work for a client on his WP website. I am only in charge of the web design so he previously bought his domain name and administered his web server.
He sent me the link https://www.dupaul.ca/wp-admin to start designing but I can not access to it, I always have a message as Safari can’t reach the page. I tried on Google chrome and firefox too, after loading for a while I got the same message. The thing is I can reach the WP admin page by my cellphone, and my client can reach the page by several computers – even not his ones.

I tried cleaning cookies and everything recommended by the Safari help page, nothing works. Please help me solving this !

Thank you

The page I need help with: [log in to see the link]