diff --git a/certbot_dns_koumbit/dns_koumbit.py b/certbot_dns_koumbit/dns_koumbit.py
index 6a29b0a..3246a4c 100644
--- a/certbot_dns_koumbit/dns_koumbit.py
+++ b/certbot_dns_koumbit/dns_koumbit.py
@@ -200,13 +200,13 @@ class AlternCInterface:
         csrf_token = self.extract_csrf_token(response.text)
 
         sub_domains = self.subdomain_regex.findall(response.text)
-        sub_domain_id = [x for x in sub_domains if x[0] == domain][0][1]
+        sub_domain_id = [x for x in sub_domains if x[0] == f"{source}.{domain}"][0][1]
 
         response = requests.post(
             url=self.base_url + "/dom_subdel.php",
             data={
                 "csrf": csrf_token,
-                "sub_domain_id": "0",
+                "sub_domain_id": sub_domain_id,
                 "confirm": "Oui"
             },
             cookies=self.cookies,