diff --git a/admin_manual/configuration_server/reverse_proxy_configuration.rst b/admin_manual/configuration_server/reverse_proxy_configuration.rst
index 97d1df467..e870a19d2 100644
--- a/admin_manual/configuration_server/reverse_proxy_configuration.rst
+++ b/admin_manual/configuration_server/reverse_proxy_configuration.rst
@@ -135,6 +135,9 @@ or
   rewrite ^/\.well-known/carddav https://$server_name/remote.php/dav/ redirect;
   rewrite ^/\.well-known/caldav https://$server_name/remote.php/dav/ redirect;
 
+When using NGINX Proxy Manager, the entry ``proxy_hide_header Upgrade;`` must be added in the *"Advanced Settings"*
+of the proxy host under *"Custom Nginx Configuration"*, otherwise mobile devices (iPad, iPhone etc.) will simply receive the Error Message "Connection Closed".
+
 Caddy
 ^^^^^
 ::