3D FlipBook - Plugin Stopped Working while on VPN

Hello!

We have have been using 3DFlipBook for a couple of years now. We have updated recently, but now whenever a user attempts to go to the area in the wp-admin to upload a new flipbook, it automatically redirects us to the input License page. On that page, our License is shown as activated, but will not let us deactivate, it just gives us an Error: undefined message. Right now we are unable to upload anything since updating.

UPDATE: I just discovered that if we are off of the VPN, the plugin will work as expected. Looks like accessing: https://test1.real3dflipbook.net/verify.php is problematic. This plugin always worked on OR off the VPN, previously.

Any ideas?