I'm unable to connect my Honda Finance account with Quicken Mac. I noticed that a possible cause for the "website unavailable" is because the URL has changed and you're still using an old one.
Your login/connect screen is showing the wrong URL for Honda Finance login (i.e. hondafinancialservices.com) [See circled yellow URL in screenshot]. If you go to that URL in a browser, you’ll notice it redirects you to honda.americanhondafinance.com. I suspect the inability to find your site is because you’re using the wrong URL. Can you change the account connection to use the new URL honda.americanhondafinance.com instead and see if that addresses the problem.
The error screen shot below: