diff --git a/api/main.py b/api/main.py
index 6d23f6b7..dec4f4f3 100644
--- a/api/main.py
+++ b/api/main.py
@@ -895,7 +895,13 @@ def _build_events_query(query_params: dict) -> tuple:
 
     if from_ts:
         if isinstance(from_ts, str):
-            from_ts = datetime.fromisoformat(from_ts)
+            try:
+                from_ts = datetime.fromisoformat(from_ts)
+            except ValueError as exc:
+                raise HTTPException(
+                    status_code=status.HTTP_400_BAD_REQUEST,
+                    detail="Invalid 'from' parameter, must be an ISO 8601 datetime"
+                ) from exc
         query_params['timestamp'] = {'$gt': from_ts}
     if path:
         query_params['data.path'] = {'$regex': path}
diff --git a/scripts/usermanager.py b/scripts/usermanager.py
index 653c3b7f..094a6cab 100755
--- a/scripts/usermanager.py
+++ b/scripts/usermanager.py
@@ -298,14 +298,9 @@ def main():
     default_paths = "\n".join(f"  - {path}" for path in DEFAULT_CONFIG_PATHS)
     parser = argparse.ArgumentParser(
         description="KernelCI API user management helper",
-        usage=(
-            "usermanager.py [-h] [--config CONFIG] [--api-url API_URL] "
-            "[--token TOKEN] [--instance INSTANCE] [--token-label TOKEN_LABEL]\n"
-            "                <command> [<args>]\n\n"
-            "Commands:\n"
-            f"{command_list}"
-        ),
         epilog=(
+            "Commands:\n"
+            f"{command_list}\n\n"
             "Examples:\n"
             "  ./scripts/usermanager.py invite --username alice --email "
             "alice@example.org --return-token\n"