// Here's the element I'm grabbing from
    <a href="#" id="clickable" date="<?php echo htmlentities(json_encode($dateArray)) ?>" customer="<?php echo htmlentities(json_encode($customerArrayClean)) ?>">
        <i class="far fa-plus-square fa-2x"></i>
    </a>

// Here's the AJAX call
    <script>
        $(document).ready(function()
        {
            $("#clickable").click(function (e)
            {
                e.preventDefault();
                let date = $("#clickable").attr("date");
                let customer = $("#clickable").attr("customer");
                console.log(date); // OUTPUT -- ["2019-12-15","2020-01-15"]
                console.log(customer); // OUTPUT -- ["CUSTOMER 1","CUSTOMER 2","CUSTOMER 3","CUSTOMER 4"]
                $.ajax
                ({
                    type: "POST",
                    url: "./reconciler_process_customers_testing.php",
                    data: {
                        date: date,
                        customer: customer
                    },
                    success: function(html)
                    {
                        if (html.success == true) {
                            alert("WORKED");
                        }
                    },
                    error: function()
                    {
                        alert("DIDNT WORK...YET");
                    }
                });
            });
        });
    </script>

// Here's the arrays being decoded
    $dateArray = json_decode($_POST['date'], true);
    $customerArray = json_decode($_POST['customer'], true);