Search autocomplete with PHP and Jquery with Database

Question

Good afternoon,

I’m trying to make an autocomplete, I followed some tutorials on the internet and here, but I think I’m sinning in some detail. My input in index.php

<div class="container d-flex justify-content-center" >

    <div class="col-lg-6">
        <form action="" method="post">
            <div class="input-group">

                <input type="text" class="form-control" placeholder="Digite aqui o seu problema com palavras chaves" name="titulo" autocomplete="off" autofocus="" required="" id="auto">
                <span class="input-group-btn" style="padding-left: 10px">
                    <button class="btn btn-success" type="submit">Pesquisar</button>
                </span>


            </div>
        </form>
    </div>


</div>

Javascript in index.php

    <script type="text/javascript">
        $(function() {

    //autocomplete
    $("#auto").autocomplete({
        source: "procura.php",
        minLength: 1
    });             
});
</script>

php search.

    <?php
include 'conexao.php';
$titulo = $_GET['titulo'];


    $return_arr = array();

     echo   $sql = "SELECT * FROM artigos where titulo = '%". $titulo  ."%'";
        $busca = oci_parse($conexao, $sql);
        oci_execute($busca);

        while($dados = oci_fetch_array($busca)) {
            $return_arr[] =  $dados['TITULO'];
        }

    /* Toss back results as json encoded array. */
    echo json_encode($return_arr);

?>

Something’s not adding up, thank you!