PHP: PDO throws SQL Syntax Error with bound params

I've read many of the other questions related to this issue, but I simply can't get to find my mistake. Here's my statement:

INSERT INTO ventas (`bodegaid`, `clienteid`, `usuarioid`, `tipodepagoid`, `fecha`, `numfact`, `serie`)
VALUES (:bodegaid, :clienteid, :usuarioid, :tipodepagoid, :fecha, :numfact, :serie)

Then I get the following error

SQLSTATE[42000]: Syntax error or access violation: 1064
You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax
to use near ':bodegaid, :clienteid, :usuarioid, :tipodepagoid,
:fecha, :numfact, :serie)' at line 1

From what I've read, this can happen when you use a reserved word as the column but that's not my case (unless I missed one but I don't think so). The table and all the columns are correct.

Are there any other reasons that could cause this error? I'm almost sure this is not about a syntax error. I've been trying to fix this for hours and I think it's probably about a silly thing I'm missing out.

Here's my PHP function, I get the $new_item from POST parameters. I have also checked that they are correctly being sent from the form:

function doVenta(){
    $app = \Slim\Slim::getInstance();
    $new_item = $app->request->post();
    $sql = "INSERT INTO ventas (`bodegaid`, `clienteid`, `usuarioid`, `tipodepagoid`, `fecha`, `numfact`, `serie`)
            VALUES (:bodegaid, :clienteid, :usuarioid, :tipodepagoid, :fecha, :numfact, :serie)";

    try {
        $db = getConnection();
        $db->beginTransaction();
        $stmt = $db->query($sql); 

        $columns = getColumns('ventas');

        foreach($new_item as $col => $val){
            $paramN = ":".$col;
            $stmt->bindValue($paramN, $val);
        }
        $stmt->execute();
        $db->lastInsertId();

        $db->commit();
    } catch(PDOException $e){
        echo errorMsg($e->getMessage());
    }

    //echo json_encode($new_item);
}

And this is the connection method, I'm using PDO:

function getConnection() {
    $dbhost="localhost";
    $dbuser="root";
    $dbpass="root";
    $dbname="inventarios";

    $dbh = new PDO("mysql:host=$dbhost;dbname=$dbname", $dbuser, $dbpass);  
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    return $dbh;
}