Can't connect Wordpress to account: 404 at wpredirect.constantcontact.com

I have been trying to connect my Wordpress plugin to my Constant Contact account, following the instructions in https://knowledgebase.constantcontact.com/articles/KnowledgeBase/10054-WordPress-Integration-with-Constant-Contact?lang=en_US. However at step 6, when I click to connect, it sends me to a long URL at wpredirect.constantcontact.com which shows a 404 error.

Am I doing something wrong, or is there an error at CC's site? When I look at the homepage for wpredirect.constantcontact.com I get errors too, so I wonder if something is misconfigured on CC's end.

Thanks in advance for any advice!