The flippingbook builder says there is a problem in the tab plugin.
I had a look on your page and found that very possible reason of your issue is javascript error raised in
www.dertec.com/newsite/media/tabs/js/script.min.js?v=8.1.1.p
file. When this error happens then all javascript stops. Since flipbook is loaded after your file with error then it does not start to execute. Please see screenshot.
I am not sure why it is throwing an error in your setup...
Can you give me (super) admin and (s)ftp access so I can take a look?
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