Error 403 in infinite scroll with jQuery, AJAX and PHP

I'm doing an infinite scroll with jQuery, AJAX and PHP. I have all the code and it does not give me any error, but it only gives me an error when I try to access the multimedia files for the scroll data, could there be an error in my code?

jQuery:

<div class="col-md-10 col-sm-12 offset-md-1 mb-4 results">

</div>
<script type="text/javascript">
            var start = 0;
            var limit = 5;
            var reachedMax = false;

            $(window).scroll(function () {
                if ($(window).scrollTop() == $(document).height() - $(window).height())
                    getData();
            });

            $(document).ready(function () {
               getData();
            });

            function getData() {
                if (reachedMax)
                    return;

                $.ajax({
                   url: 'publicaciones.php',
                   method: 'POST',
                   dataType: 'text',
                   data: {
                       getData: 1,
                       start: start,
                       limit: limit
                   },
                   success: function(response) {
                        if (response == "reachedMax")
                            reachedMax = true;
                        else {
                            start += limit;
                            $(".results").append(response);
                        }
                    }
                });
            }
</script>

PHP:

<?php
    if(isset($_POST['getData']))
    {
        include ('../conexion.php');

        $start = mysqli_real_escape_string($conexion,$_POST['start']);
        $limit = mysqli_real_escape_string($conexion,$_POST['limit']);

        $consulta = mysqli_query($conexion, "SELECT * FROM publicaciones ORDER BY id_pub DESC LIMIT $start, $limit");   

        if(mysqli_num_rows($consulta) > 0)
        {
            $response = "";

            while($data = mysqli_fetch_array($consulta)) {
                $response .= "      
                    <div class='card mt-3 border-0 rounded-0'>
                        <div class='card-body'>
                            <div class='row'>
                                <div class='col-sm-2'>
                                    <div class='img-user rounded-circle'>
                                        <img class='img-fluid-pub' src='../avatars/".$data['avatar']."' alt='User Image'>
                                    </div>
                                </div>
                                <div class='col-sm-10'>
                                    <h3 class='text-muted' onclick='location.href='perfil.php?id='".$data['id']."'>".$data['usuario']."</h3><h3>Seguir</h3>
                                    <p>".$lista['fecha']."</p>
                                    <p>".$lista['titulo']." Me gusta</p>
                                    <p id='descripcion'>".$lista['descripcion']."</p>
                                    <p class='leermas' onclick='leerMas(this);'>Leer más...</p>             
                                    <video controls>
                                        <source src='../anadir-publicacion/publicaciones/".$lista['video']."' type='video/mp4'>
                                        Your browser does not support HTML5 video.
                                    </video>
                                    <p>Kcal: ".$lista['kcal']." CarbHid: ".$lista['carbohidratos']." Prot: ".$lista['proteinas']." Gras: ".$lista['grasas']." Tiempo: ".$lista['tiempo']." Personas: ".$lista['personas']." Dinero aprox: ".$lista['precio']."€ Categoría: ".$lista['categoria'];"</p>
                                </div>
                            </div>
                        </div>
                    </div>
                ";
            }
            exit($response);
        }
        else 
            exit('reachedMax');
    }   
?>