diff --git a/core/tidal_download_client.py b/core/tidal_download_client.py
index a7efb40f..6ae2027e 100644
--- a/core/tidal_download_client.py
+++ b/core/tidal_download_client.py
@@ -95,6 +95,16 @@ HLS_MAP_TAG_RE = re.compile(r'#EXT-X-MAP:.*URI="([^"]+)"')
 from core.download_plugins.base import DownloadSourcePlugin
 
 
+def _looks_like_json_decode_error(exc: Exception) -> bool:
+    name = exc.__class__.__name__.lower()
+    message = str(exc).lower()
+    return (
+        "jsondecodeerror" in name
+        or "expecting value" in message
+        or "could not decode json" in message
+    )
+
+
 class TidalDownloadClient(DownloadSourcePlugin):
     """
     Tidal download client using tidalapi.
@@ -230,6 +240,18 @@ class TidalDownloadClient(DownloadSourcePlugin):
                 return {'status': 'error', 'message': 'Auth completed but session invalid'}
 
         except Exception as e:
+            if _looks_like_json_decode_error(e):
+                logger.error(
+                    "Tidal device auth check received a non-JSON response from Tidal's token endpoint: %s",
+                    e,
+                )
+                return {
+                    'status': 'error',
+                    'message': (
+                        "Tidal returned an invalid auth response while SoulSync was finishing login. "
+                        "Try again after disabling VPN/proxy/network filtering, then restart SoulSync if it repeats."
+                    ),
+                }
             logger.error(f"Tidal device auth check error: {e}")
             return {'status': 'error', 'message': str(e)}
 
diff --git a/tests/downloads/test_tidal_pinning.py b/tests/downloads/test_tidal_pinning.py
index 74327f37..bb4db8e9 100644
--- a/tests/downloads/test_tidal_pinning.py
+++ b/tests/downloads/test_tidal_pinning.py
@@ -61,6 +61,26 @@ def test_is_authenticated_false_when_session_check_login_raises(tidal_client_wit
     assert client.is_authenticated() is False
 
 
+def test_check_device_auth_returns_helpful_message_for_non_json_tidal_response(tidal_client_with_engine):
+    client, _ = tidal_client_with_engine
+
+    class FakeFuture:
+        def running(self):
+            return False
+
+        def result(self, timeout=0):
+            raise ValueError("Expecting value: line 1 column 1 (char 0)")
+
+    client._device_auth_future = FakeFuture()
+    client._device_auth_link = {'verification_uri': 'https://link.tidal.com', 'user_code': 'ABCD'}
+
+    result = client.check_device_auth()
+
+    assert result['status'] == 'error'
+    assert 'invalid auth response' in result['message']
+    assert 'Expecting value' not in result['message']
+
+
 # ---------------------------------------------------------------------------
 # download() — filename parsing + id contract
 # ---------------------------------------------------------------------------