AJAX returning 0

I am trying to do a basic ajax function but all I can get back is a 0. Code is as follows:

In my main script.js file I have:

function populateCardAmount(){
    var cardAmt = $("#trading_card_amount").val();
        $.ajax({
            type: 'POST',
            url: '/wp-admin/admin-ajax.php',
            data: {
                action: 'populate_qualified_cards',
                cardAmt: cardAmt,
            },
            success: function(data){
                console.log(data);
            },
            error: function(){
                alert('error');
            }
        });
}

And in functions.php I have:

function populate_qualified_cards(){
    $amt = $_POST['cardAmt'];
    print_r($amt);
    die();
}
add_action( 'wp_ajax_nopriv_populate_qualified_cards', 'populate_qualified_cards' );
add_action( 'wp_ajax_populate_qualified_cards', 'populate_qualified_cards' );

Help Please!!! Thank you!!