How to disable autozoom via html in iphone browsers?

Question

iPhone

Good afternoon!
There is a website page (kumantsova_com/price) with a booking form (name, email and text). A modal window pops up when you click on the "Book" button, and if you click on the text input field on an iPhone (safari), the form floats somewhere and you see a black screen. If you close the system input keyboard, the form reappears.
The modal window is implemented through a slider script that is used for images.
A similar glitch was fixed with normal forms on the site and it was treated by setting the font size of the input test to 16px or by setting user-scalable=0 through the meta tag, but in our case this for some reason did not help solve the problem.
It is not necessary to recommend funcybox. Interested in solving the problem with this script. Tell me where to dig? Check what?
Thank you!