Warning: PDOStatement :: execute () expects parameter 1 to be array, string given

I am trying to get a json from a Database, the problem that gives me the error in the title how can I solve it?


 if (isset($_GET("provincia"))) {
if (empty($_GET('ccaa'))) {
  $dbConn->exec("set names utf8");
  $sql="SELECT provincia FROM cp WHERE ccaa = :ccaa";
  $consulta = $dbConn->prepare($sql);
  header("HTTP/1.1 200 OK");
  echo json_encode($consulta->fetchAll());