Note that Wix does not provide support for third party code that it hasn’t had the chance to fully test out itself, therefore if you have any issues with it then you need to go back to your third party provider, in this case Booking.com and get help from their own support to integrate it into Wix.
Although to be honest, you are much better and more secure, using their own API and exposing your site to it through Wix Fetch or Wix HTTP Functions. https://developers.booking.com/api/index.html