Required nonce value is not here

Hello, if i use the Nitropack plugin in combination with the booking system of the theme Kingo of Themegoods (https://themeforest.net/item/kingo-landing-booking-for-small-businesses/23385668), this error happens:

“required nonce value is not here, please let the developer know”

Image of the error: https://ibb.co/9vtY8ck

The developer of the theme told me to contact the NitroPack developers because according to him it is not a problem of his theme.

Can you kindly help me to solve this issue?

I have momentarily deactivated Nitropack in the website.

Thanks a lot!

The page I need help with: [log in to see the link]