diff --git a/netx_api/ume_alarm_ws.py b/netx_api/ume_alarm_ws.py
index 0004f46..7f3476a 100644
--- a/netx_api/ume_alarm_ws.py
+++ b/netx_api/ume_alarm_ws.py
@@ -162,7 +162,12 @@ def establish_alarm_subscription_manual(client: UMEClient, db: Session) -> dict[
         if not orphan_id:
             raise
         _ws_log.warning("establish: UME reports existing subscription id=%s, deleting then retry", orphan_id)
-        _delete_subscription_on_ume(client, orphan_id)
+        try:
+            _delete_subscription_on_ume(client, orphan_id)
+        except RuntimeError as del_exc:
+            raise RuntimeError(
+                f"ume_orphan_subscription_delete_failed:id={orphan_id}:{str(del_exc)[:180]}"
+            ) from del_exc
         sub_id, uri = client.establish_alarm_subscription(topic=topic)
     save_subscription(db, subscription_id=sub_id, wss_uri=uri, topic=topic)
     db.commit()
diff --git a/netx_api/ume_client.py b/netx_api/ume_client.py
index c6afdc5..f526a0c 100644
--- a/netx_api/ume_client.py
+++ b/netx_api/ume_client.py
@@ -23,6 +23,21 @@ def _coerce_list(value: Any) -> list[Any]:
     return value if isinstance(value, list) else []
 
 
+def _parse_json_response(resp: httpx.Response) -> dict[str, Any]:
+    """Parse JSON body; UME often returns 204/empty body on successful DELETE operations."""
+    raw = str(resp.text or "").strip()
+    if not raw:
+        return {}
+    try:
+        return _coerce_dict(resp.json())
+    except json.JSONDecodeError as exc:
+        if resp.is_success:
+            return {}
+        raise RuntimeError(
+            f"ume_request_failed:{int(resp.status_code)}:non_json_body:{raw[:200]}"
+        ) from exc
+
+
 @dataclass
 class RequestDiagnostics:
     method: str
@@ -422,8 +437,9 @@ class UMEClient:
                     marker=marker,
                     is_end_of_reply=is_end_of_reply,
                 )
-                raise RuntimeError(f"ume_request_failed:{resp.status_code}:{resp.text[:240]}")
-            data = _coerce_dict(resp.json())
+                body_snip = raw[:240] if (raw := str(resp.text or "").strip()) else "(empty body)"
+                raise RuntimeError(f"ume_request_failed:{m} {path} {resp.status_code}:{body_snip}")
+            data = _parse_json_response(resp)
             diag = RequestDiagnostics(
                 method=m,
                 path=path,
@@ -437,7 +453,7 @@ class UMEClient:
         except Exception as exc:
             if isinstance(exc, RuntimeError):
                 raise
-            raise RuntimeError(f"ume_request_failed:{str(exc)[:240]}") from exc
+            raise RuntimeError(f"ume_request_failed:{m} {path}:{str(exc)[:200]}") from exc
 
     def request_json(
         self,
@@ -477,8 +493,9 @@ class UMEClient:
                     marker=marker,
                     is_end_of_reply=is_end_of_reply,
                 )
-                raise RuntimeError(f"ume_request_failed:{resp.status_code}:{resp.text[:240]}")
-            data = _coerce_dict(resp.json())
+                body_snip = raw[:240] if (raw := str(resp.text or "").strip()) else "(empty body)"
+                raise RuntimeError(f"ume_request_failed:{m} {path} {resp.status_code}:{body_snip}")
+            data = _parse_json_response(resp)
             diag = RequestDiagnostics(
                 method=m,
                 path=path,
@@ -492,7 +509,7 @@ class UMEClient:
         except Exception as exc:
             if isinstance(exc, RuntimeError):
                 raise
-            raise RuntimeError(f"ume_request_failed:{str(exc)[:240]}") from exc
+            raise RuntimeError(f"ume_request_failed:{m} {path}:{str(exc)[:200]}") from exc
 
     def _extract_named_list(self, payload: dict[str, Any], keys: list[str]) -> list[dict[str, Any]]:
         target_keys = {str(k).lower() for k in keys}
diff --git a/tests/test_ume_sync.py b/tests/test_ume_sync.py
index e81d194..ef14fa8 100644
--- a/tests/test_ume_sync.py
+++ b/tests/test_ume_sync.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import json
 import unittest
 from typing import Any
 from unittest.mock import patch
@@ -10,7 +11,7 @@ from sqlalchemy.orm import sessionmaker
 from netx_api.db import Base
 from netx_api.main import _extract_ume_raw_group_field, _serialize_ume_alarm_raw_row, sql_ume_query, ume_alarms_fields
 from netx_api.models import UmeAlarmCurrent, UmeInventoryNE
-from netx_api.ume_client import UMEClient
+from netx_api.ume_client import UMEClient, _parse_json_response
 from netx_api import ume_alarm_ws
 from netx_api.models import UmeAlarmSubscription
 from netx_api.ume_alarm_subscription_store import clear_subscription, load_subscription, save_subscription
@@ -175,6 +176,39 @@ class UMEClientTests(unittest.TestCase):
         self.assertEqual(sub_id, "3282ac78-b38a-4242-81d2-cc5b77c28ef8")
         self.assertIn("wss://", uri)
 
+    def test_parse_json_response_accepts_empty_success_body(self):
+        class _Resp:
+            is_success = True
+            status_code = 204
+            text = ""
+
+            def json(self):
+                raise json.JSONDecodeError("Expecting value", "", 0)
+
+        self.assertEqual(_parse_json_response(_Resp()), {})  # type: ignore[arg-type]
+
+    def test_delete_alarm_subscription_empty_response(self):
+        from time import time as _time
+
+        client = UMEClient(base_url="https://ume.local:18014", username="u", password="p", verify_tls=False)
+        client._token_value = "token-1"
+        client._token_expires_at = _time() + 3600
+
+        class _Resp:
+            is_success = True
+            status_code = 204
+            text = ""
+            headers: dict[str, str] = {}
+
+            def json(self):
+                raise json.JSONDecodeError("Expecting value", "", 0)
+
+        def _fake_request(method: str, path: str, *, params=None, body=None):
+            return _parse_json_response(_Resp()), None  # type: ignore[arg-type]
+
+        client.request_json = _fake_request  # type: ignore[method-assign]
+        client.delete_alarm_subscription("sub-to-delete")
+
     def test_delete_alarm_subscription(self):
         from time import time as _time