diff --git a/idhub/management/commands/send_mail_admins.py b/idhub/management/commands/send_mail_admins.py
index eae3e41..a878456 100644
--- a/idhub/management/commands/send_mail_admins.py
+++ b/idhub/management/commands/send_mail_admins.py
@@ -27,7 +27,7 @@ class Command(BaseCommand):
         """
         Send a email when a user is activated.
         """
-        url_domain = f"https://{}/".format(settings.DOMAIN)
+        url_domain = "https://{}/".format(settings.DOMAIN)
         context = {
             "domain": url_domain,
         }