diff --git a/changelog.d/fixes/13832-credential-allowlist-diagnostic.md b/changelog.d/fixes/13832-credential-allowlist-diagnostic.md
new file mode 100644
index 0000000000..619f323fb3
--- /dev/null
+++ b/changelog.d/fixes/13832-credential-allowlist-diagnostic.md
@@ -0,0 +1 @@
+- **fix(sse):** when a gateway API key's `allowed_connections` / quota scope hides every connection of a provider, chat now answers `403` naming that scope instead of the generic `No active credentials for provider: X` — which was indistinguishable from "never configured" even though `/test` and `/sync-models` kept working on the same connection ([#13832](https://github.com/diegosouzapw/OmniRoute/issues/13832))
diff --git a/src/sse/handlers/chatHelpers.ts b/src/sse/handlers/chatHelpers.ts
index 8a18d01c1d..b47c0037ac 100644
--- a/src/sse/handlers/chatHelpers.ts
+++ b/src/sse/handlers/chatHelpers.ts
@@ -825,6 +825,23 @@ export function handleNoCredentials(
       status === "credits_exhausted" ? HTTP_STATUS.PAYMENT_REQUIRED : HTTP_STATUS.UNAUTHORIZED;
     return errorResponse(httpStatus, message);
   }
+  if (credentials?.blockedByKeyPolicy) {
+    // #13832: the provider HAS active connections — they were filtered out by the
+    // gateway API key's connection allowlist (`allowed_connections`) or its quota
+    // scope, so the pool arrived empty and the generic "No active credentials"
+    // below was indistinguishable from "this provider was never configured". That
+    // cost the reporter a full investigation: their key passed `/test` and synced
+    // 82 models (both address the connection by id and never consult the key's
+    // scope), while chat kept failing. The classic shape is a key minted before
+    // the provider existed, which is why older providers keep working on it.
+    // 403, not 401: the credential is fine, this principal is not allowed to use it.
+    const count = credentials.blockedCount || 1;
+    const message =
+      `[${provider}] ${count} connection(s) exist but are excluded by this API key's ` +
+      `connection allowlist / quota scope — add them to the key in the dashboard, or use a key without that scope`;
+    log.warn("AUTH", message);
+    return errorResponse(HTTP_STATUS.FORBIDDEN, message);
+  }
   if (!excludeConnectionId) {
     // Ported from upstream decolua/9router#336 (Ibrahim Ryan): surface as 404
     // NOT_FOUND instead of 400 BAD_REQUEST so combo routing can fall through to
diff --git a/src/sse/services/auth.ts b/src/sse/services/auth.ts
index 42554e6d30..2658f8d1fb 100644
--- a/src/sse/services/auth.ts
+++ b/src/sse/services/auth.ts
@@ -1389,9 +1389,16 @@ export async function getProviderCredentials(
       let allConnections = (allConnectionsResults.filter(Array.isArray).flat() as unknown[])
         .map(toProviderConnection)
         .filter((conn) => conn.id.length > 0);
+      // #13832: remember how many connections the provider really has BEFORE the
+      // key-policy filter, so an empty pool can say which gate emptied it. Without
+      // this the caller only ever saw "No active credentials for provider: X",
+      // identical to "never configured" — while /test and /sync-models kept working,
+      // because they address a connection by id and never consult the key's scope.
+      const connectionsBeforeKeyPolicy = allConnections.length;
       if (allowedConnections && allowedConnections.length > 0) {
         allConnections = allConnections.filter((conn) => allowedConnections.includes(conn.id));
       }
+      const blockedByKeyPolicyCount = connectionsBeforeKeyPolicy - allConnections.length;
       if (forcedConnectionId) {
         allConnections = allConnections.filter((conn) => conn.id === forcedConnectionId);
       }
@@ -1461,6 +1468,16 @@ export async function getProviderCredentials(
         return geminiEnvCredentials;
       }
       invalidateManagedLease(options, "CONNECTION_INELIGIBLE");
+      if (blockedByKeyPolicyCount > 0) {
+        // #13832: the pool is empty only because the calling key's allowlist /
+        // quota scope removed every connection. Say so instead of returning the
+        // bare null that becomes "No active credentials for provider: X".
+        log.warn(
+          "AUTH",
+          `${provider} | ${blockedByKeyPolicyCount} connection(s) hidden by the API key's allowed_connections/quota scope`
+        );
+        return { blockedByKeyPolicy: true, blockedCount: blockedByKeyPolicyCount };
+      }
       log.debug("AUTH", `No credentials for ${provider}`);
       return null;
     }
diff --git a/tests/unit/chat-helpers.test.ts b/tests/unit/chat-helpers.test.ts
index 21ac50fa27..24a2b7ed03 100644
--- a/tests/unit/chat-helpers.test.ts
+++ b/tests/unit/chat-helpers.test.ts
@@ -778,3 +778,32 @@ test("resolveModelOrError returns model_not_found error for unrecognised bare mo
   assert.match(json.error.message, /Unable to determine provider/i);
   assert.match(json.error.message, /completely-unknown-model-xyz/i);
 });
+
+test("handleNoCredentials names the API key's connection allowlist as the reason (#13832)", async () => {
+  // #13832: connections for the provider exist and are active, but the gateway API
+  // key's allowed_connections / quota scope filtered every one of them out, so the
+  // pool arrived empty. The old generic "No active credentials for provider: nvidia"
+  // is indistinguishable from "never configured" — the reporter had a key that
+  // passed /test and synced 82 models, and no message ever mentioned the allowlist.
+  const blocked = handleNoCredentials(
+    { blockedByKeyPolicy: true, blockedCount: 2 },
+    null,
+    "nvidia",
+    "nvidia/nemotron",
+    null,
+    null,
+    undefined,
+    /* isCombo */ false
+  );
+
+  assert.equal(blocked.status, 403);
+  const blockedJson = (await blocked.json()) as { error?: { message?: string } };
+  const message = blockedJson.error?.message ?? "";
+  assert.match(message, /nvidia/);
+  assert.match(message, /2 connection\(s\)/);
+  assert.match(
+    message,
+    /allowlist|quota scope/i,
+    "the operator must be told WHICH gate hid the connections"
+  );
+});