booking-date.js

// booking date  check in > check out
// add the two class 'in-date' & 'out-date'

$( document ).ready(function() {
    var check_in = flatpickr(".in-date",{dateFormat: "d/m/Y",});
    var check_out = flatpickr(".out-date",{dateFormat: "d/m/Y",});
    
    check_in.element.addEventListener("change", function(){

        check_out.set( "minDate" , check_in.element.value );
    });
    
    check_out.element.addEventListener("change", function(){
        check_in.set( "maxDate" , check_out.element.value );
    });
    
});

This is excellent. Thank you.
I wonder if it'd be possible to show an error message if the user tries to select an out date that is before the in date? On desktop it greys it out, which is great. But on Android and iPhone the mobile apps use their own calendar picker and so it doesn't show greyed out dates. If you select an out date that is before an in date on mobile it just clears your selection.