Drupal + Mailchimp API : create campaign with an existing template - php

Question

I'm trying to create a campaign with the Mailchimp PHP API in a custom Drupal module, but i fail to use an existing template.
I am sure of my template id in the request, but the id is always 0 in the response.
What is the correct request payload to reuse a template ?
I just want to reuse a very simple template. For now, there's no specific text for the campaign, i'll try to insert a text pattern when i'll be able to use the correct template.
Thanks in advance.
Here is my current code :
function mymodule_templates_list()
{
$mailchimpPath = realpath(__DIR__ . '/../../libraries/mailchimp');
require_once $mailchimpPath . '/src/Mailchimp.php';
require_once $mailchimpPath . '/src/Mailchimp/Templates.php';
$mailchimp = new Mailchimp('my-api-key');
$templatesService = new Mailchimp_Templates($mailchimp);
$list = $templatesService->getList(
array(
'user' => true,
'gallery' => false,
'base' => false,
),
array(
'include_drag_and_drop' => true,
)
);
dpm($list); // just to verify the template ID
$campaignService = new Mailchimp_Campaigns($mailchimp);
$response = $campaignService->getList();
dpm($response);
$options = array(
"list_id" => 'my-list-id', // this is OK, correct list used in the response
"subject" => "My subject", // OK
"from_email" => "mymail#dev.null", // OK
"from_name" => "Site name", // OK
"to_name" => '',
'template_id' => 123456, // KO : 0 in the response
);
$content = array(
"text" => "dunno what to use here",
"url" => 'dunno what to use here',
"archive" => "dunno what to use here",
);
$response = $campaignService->create('regular', $options, $content);
dpm($response);
return '';
}