OK, after seeing this, and now testing, I see where the issue is. Your example states that it looks for https://domainhere.com to verify. However, for the WHMCS System URL setting, you have the following instructions for this field: The URL to your WHMCS installation (SSL Recommended) eg. https://www.example.com/members/.
My guess is that everyone seeing this issue, much like myself, has always had that field filled with https://www.mydomain.com/whmcsdirectory/'>https://www.mydomain.com/whmcsdirectory/ as you instruct. Once I removed the directory from this setting to just have https://www.mydomain.com there, the check for Website SSL passes. So, either you need to update the Website SSL option to account for people following your instructions for that setting, or update the instructions for that page, assuming not having the full URL to the WHMCS directory doesn't cause some other issue.