return [
            '#theme' => 'webservices_client',
            '#id' => $infos_clients->body->id,
            '#nom' => $infos_clients->body->nom,
 ];

Array
(
    [0] => stdClass Object
        (
            [numero] => 625
            [dateDebut] => 2018-09-27T09:21:54.5746973
        )

    [1] => stdClass Object
        (
            [numero] => 468
            [dateDebut] => 2018-05-17T16:50:33.6357383
        )

)

return [
            '#theme' => 'webservices_informations',
            '#myvariable' => $response,
       ];

function webservices_informations_theme(array $existing, $type, $theme, $path) {
    return array(
        'webservices_informations' => array(
            'variables' => array(
                'myvariable' => NULL,
            ),
        ),
    );
}

{% for key, value in myvariable %}
            Key : {{ key }}<br>
            Name : {{ value.id }}<br>
{% endfor %