Correct me if I'm wrong. You can access the custom CCP URL, but you can't access Connect because access to Amazon Connect is blocked from the custom CCP in S3.
If this is the case, in the "Approved Domains" section, add the URL of your S3 bucket or the domain from which you intend to connect to Amazon Connect.
You can find the reference at this link https://docs.aws.amazon.com/connect/latest/adminguide/app-integration.html
