MySQL Fatal Error bind param

Question

i have this code:

<?php

if (isset($_POST['agregar-admin'])) {
    $nombre = $_POST['nombre'];
    $usuario = $_POST['usuario'];
    $password = $_POST['contraseña'];

    $opciones = array(
        'cost' => 12
    );

    $password_hashed = password_hash($password, PASSWORD_BCRYPT, $opciones);

    try {
        include_once 'funciones/funciones.php';
        $stmt = $conn->prepare("INSERT INTO admins (nombre, usuario, password) VALUES (?, ?, ?)");
        $stmt->bind_param("sss", $nombre, $usuario, $password_hashed);
        $stmt->execute();
        $stmt->close();
        $conn->close();

    } catch (Exception $e) {
        echo "Error: " . $e->getMessage();
    }



}

I'm trying to insert into db from a form, but i get this error:

Fatal error: Call to a member function bind_param() on boolean in C:\wamp64\www\gdlwebcamp\admin\insertar-admin.php on line 17

I have investigated and it is because prepare return false (i think so), tried changing thinks and trying one by one but doesn't work, how can i fix it? Thanks.