btcpayserver/BTCPayServer/wwwroot/payment-request-admin/main.js

$(document).ready(function() {

    $(".richtext").summernote({
        minHeight: 300
    });
    $(".datetime").each(function () {
        var element = $(this);
        var min = element.attr("min");
        var max = element.attr("max");
        var defaultDate = element.attr("value");
        element.flatpickr({
            enableTime: true,
            minDate: min,
            maxDate: max,
            defaultDate: defaultDate,
            dateFormat: 'Z',
            altInput: true,
            altFormat: 'J F Y H:i',
            time_24hr: true,
            parseDate: function (date) {
                return moment(date).toDate();
            }
        });
    });

});