Hi Donald,

the problem is due to the fact that the Pingomatic website https://pingomatic.com/ has the SSL certificate that is expired (image visible below)
I contacted them reporting this, but they still have not updated the SSL certificate.

In this case to solve you have to navigate to the website https://pingomatic.com/ in your browser and grant access and an exception.
After that you can ping successfully on your site https://usncva.org

Even better, it would be adding a permanent exception in your browser for https://pingomatic.com/ so that you won't have to do this again in future.

Regards,
John