Apologies for the issues, but I also tested and was unable to find any problem with Boxtrapper. If you want to see it working login to your cpanel, go to the TEST email account and change the password. Then login to it with the Webmail option. You can see the messages that have been sent to it. I also forwarded the typical message sent when Boxtrapper is working. This shows that Boxtrapper is working.
Just to summarize, Boxtrapper (when enabled) automatically sends an email to the person who emailed that account. In the verification email, there is a LINK, that the user must click in order verify. Once they are verified, then the email is delivered. Otherwise, it will be refused. If an emailer is already on the whitelist, then boxtrapper will not activate (and send a verification email).
You have been saying that a "page cannot be displayed" - we need better information on the error message that you're seeing. I'm sorry that we don't have any direct way to view your computer (please email firstname.lastname@example.org to suggest this option), but we currently have no way to do this. If you can provide more information such as an error message or more information to duplicate the error then we can investigate the issue. Currently, we cannot duplicate the problem. Remember that the Boxtrapper option can only be used when its enabled for the specific email account. For more information, please check out fighting spam with Box Trapper
If you have any further questions or concerns, please let us know.