diff --git a/src/SubscribeMe/Subscriber/SendInBlueSubscriber.php b/src/SubscribeMe/Subscriber/SendInBlueSubscriber.php
index 3497cfd..fec3610 100644
--- a/src/SubscribeMe/Subscriber/SendInBlueSubscriber.php
+++ b/src/SubscribeMe/Subscriber/SendInBlueSubscriber.php
@@ -19,7 +19,7 @@ public function subscribe(string $email, array $options, array $userConsents = [
     {
         $body = [
             'email' => $email,
-            'listIds' => [$this->getContactListId()]
+            'listIds' => [(int) $this->getContactListId()]
         ];
 
         if (count($options) > 0) {