Los datos no se envían a la base de datos SQL usando MySQLi y PHP

Es posible que deba verificar los nombres de las variables y ajustarlos a su gusto. Use una declaración preparada para evitar la inyección de sql.

if(isset($_POST['submit'])){

    $conn = new mysqli($servername, $username, $password, $dbname);
    // Check connection can be established
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    }
    $target_path = '';
    if (!empty($_FILES["uploadedimage"]["name"])) {
        $file_name=$_FILES["uploadedimage"]["name"];
        $temp_name=$_FILES["uploadedimage"]["tmp_name"];
        $imgtype=$_FILES["uploadedimage"]["type"];
        $ext= GetImageExtension($imgtype);
        $imagename= $_FILES['uploadedimage']['name'];
        $target_path = "images/".$imagename;
    }

    $date = $_POST['date'];
    $retrace = $_POST['retrace'];
    $start_of_swing_trade = $_POST['start_of_swing_trade'];
    $end_of_swing_trade = $_POST['end_of_swing_trade'];
    $bull_flag = $_POST['bull_flag'];
    $bear_flag = $_POST['bear_flag'];
    $ema_crossover = $_POST['ema_crossover'];
    $trading_instrument = $_POST['trading_instrument'];

    if($date !=''||$trading_instrument !=''){

        $sql = "INSERT into charts (charts_URL, charts_date, charts_retrace, charts_start_of_swing_trade, charts_end_of_swing_trade, charts_bullflag, charts_bearflag, charts_ema_crossover, charts_trading_instrument) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)";
        // s = string, i = integer, d = double, b = blob
        //preparing statement
        $stmt = $conn->prepare($sql);
        if(!$stmt){ exit("prepare failed");}
        //binding param
        $bind = $stmt->bind_param('sssssssss',$target_path, $date, $retrace, $start_of_swing_trade, $end_of_swing_trade, $bull_flag, $bear_flag, $ema_crossover, $trading_instrument);
        if(!$bind){ exit("bind failed");}
        //will return 0 if fail
        if($stmt->execute() != 0){

            echo "New record created successfully";
        }else{ echo "Failed to insert new record";}

    }
//close connection
$conn->close();
}