diff --git a/gateway/platforms/base.py b/gateway/platforms/base.py
index 1a044d1521f7d..581f08850b22b 100644
--- a/gateway/platforms/base.py
+++ b/gateway/platforms/base.py
@@ -2586,6 +2586,7 @@ def classify_send_error(exc: Optional[BaseException], error_text: str = "") -> s
         or "not enough rights" in blob
         or "have no rights" in blob
         or "not a member" in blob
+        or "target_not_allowed" in blob
     ):
         return "forbidden"
     if any(s in blob for s in _CHAT_LEVEL_NOT_FOUND_SUBSTRINGS) or any(
diff --git a/tests/gateway/test_dead_targets.py b/tests/gateway/test_dead_targets.py
index a1a34fd41b5ba..6e45316f05c74 100644
--- a/tests/gateway/test_dead_targets.py
+++ b/tests/gateway/test_dead_targets.py
@@ -105,6 +105,37 @@ async def test_shared_registry_is_used_when_injected(isolate):
     assert adapter.calls == []
 
 
+@pytest.mark.asyncio
+async def test_photon_target_not_allowed_marks_target_dead(isolate):
+    # A shared/free-tier Photon line permanently cannot open a new outbound
+    # thread to this target (Spectrum "target_not_allowed"). Scheduled/cron
+    # delivery only sees the raised RuntimeError text (not the adapter's
+    # structured raw_response), so classify_send_error must recognize this
+    # shape from text alone or the target retries forever on every tick.
+    message = (
+        "Photon sidecar /send returned 403 (target_not_allowed, "
+        "retryable=False): shared/free-tier Photon lines cannot initiate "
+        "outbound sends to new targets — upgrade to a dedicated line or "
+        "use another delivery channel"
+    )
+    adapter = RaisingAdapter(message)
+    router = DeliveryRouter(GatewayConfig(), adapters={Platform("photon"): adapter})
+    target = DeliveryTarget.parse("photon:900")
+
+    res1 = await router.deliver("hi", [target])
+    assert res1["photon:900"]["success"] is False
+    assert router.dead_targets.is_dead("photon", "900") is True
+    assert adapter.calls == ["900"]
+
+    # Second delivery: short-circuited, adapter NOT called again — this is
+    # the actual bug: before the fix, classify_send_error returned "unknown"
+    # for this text, so mark_dead() was never called and every cron tick
+    # re-sent to a target the sidecar had already permanently rejected.
+    res2 = await router.deliver("hi again", [target])
+    assert res2["photon:900"]["skipped"] == "dead_target"
+    assert adapter.calls == ["900"]
+
+
 # --------------------------------------------------------------------------
 # not_found blast radius: chat-level kills the chat, thread/message-level must not
 # --------------------------------------------------------------------------
diff --git a/tests/gateway/test_send_error_classification.py b/tests/gateway/test_send_error_classification.py
index 5bb69dccdb21f..0bb08a4e1fbed 100644
--- a/tests/gateway/test_send_error_classification.py
+++ b/tests/gateway/test_send_error_classification.py
@@ -29,6 +29,13 @@ class _FakeBadRequest(Exception):
         ("Forbidden: bot was blocked by the user", "forbidden"),
         ("Forbidden: user is deactivated", "forbidden"),
         ("Bad Request: not enough rights to send text messages", "forbidden"),
+        (
+            "Photon sidecar /send returned 403 (target_not_allowed, "
+            "retryable=False): shared/free-tier Photon lines cannot "
+            "initiate outbound sends to new targets — upgrade to a "
+            "dedicated line or use another delivery channel",
+            "forbidden",
+        ),
         ("Bad Request: chat not found", "not_found"),
         ("Bad Request: message to edit not found", "not_found"),
         ("Too Many Requests: retry after 12", "rate_limited"),