3D FlipBook - very slow in backend

Hi, when I'm trying to do various tasks with the plugin - e.g. add new - it takes ages to respond or process the request.

I've looked in the Network section of Developer Tools on my browser and it seems that verify.php is the cause. For example, when I just tried to add new flip book, the verify.php file took 30.07 seconds. (It says the domain was test1.real3dflipbook.net).

It's really a drag having to wait 30-60 seconds every time I want to do something with the flipbooks. Any idea why this is happening or a fix? The licence has been activated.

Thanks.