Enlighten me about the incompatibility of fancybox and VirtueMart?

Question

Joomla

The customer asked to make a callback popup module. I decided to do it on fancybox, everything worked, but later it turned out that the basket stopped working, the goods were not added and the order popup window did not appear. The problem turned out to be in the library that I added to the template. How to solve this problem, I don’t want to connect a third-party module, they write on the forums that it is difficult to position it correctly against the background of the top banner. VM version 2.6.4, Joomla 2.5.6. Maybe a glitch in the version of the library itself?