diff --git a/scripts/matrix_device_cleanup.py b/scripts/matrix_device_cleanup.py
index a21d828..0d1b7f0 100755
--- a/scripts/matrix_device_cleanup.py
+++ b/scripts/matrix_device_cleanup.py
@@ -14,6 +14,7 @@ import os
 import subprocess
 import sys
 import time
+from urllib.parse import quote
 
 import httpx
 
@@ -49,8 +50,9 @@ async def list_devices(
     client: httpx.AsyncClient, homeserver: str, headers: dict, user_id: str,
 ) -> list[dict]:
     """List all devices for a user via Synapse Admin API."""
+    encoded_user = quote(user_id, safe="")
     resp = await client.get(
-        f"{homeserver}/_synapse/admin/v2/users/{user_id}/devices",
+        f"{homeserver}/_synapse/admin/v2/users/{encoded_user}/devices",
         headers=headers,
     )
     resp.raise_for_status()
@@ -65,8 +67,9 @@ async def delete_devices_batch(
     device_ids: list[str],
 ) -> int:
     """Bulk-delete devices. Returns count deleted."""
+    encoded_user = quote(user_id, safe="")
     resp = await client.post(
-        f"{homeserver}/_synapse/admin/v2/users/{user_id}/delete_devices",
+        f"{homeserver}/_synapse/admin/v2/users/{encoded_user}/delete_devices",
         headers=headers,
         json={"devices": device_ids},
     )
@@ -186,7 +189,7 @@ def main():
     parser.add_argument(
         "--homeserver",
         default=os.environ.get("MATRIX_HOMESERVER", "https://matrix.agiliton.eu"),
-        help="Homeserver URL",
+        help="Homeserver URL (use http://CONTAINER_IP:8008 when running on the matrix VM)",
     )
     parser.add_argument("--keep", type=int, default=1, help="Number of most recent devices to keep")
     parser.add_argument("--max-age-days", type=int, default=None, help="Only delete devices older than N days")