diff --git a/extensions/matrix/src/matrix/active-client.ts b/extensions/matrix/src/matrix/active-client.ts
index a643f343b..0f309d395 100644
--- a/extensions/matrix/src/matrix/active-client.ts
+++ b/extensions/matrix/src/matrix/active-client.ts
@@ -1,5 +1,5 @@
 import type { MatrixClient } from "@vector-im/matrix-bot-sdk";
-import { DEFAULT_ACCOUNT_ID } from "openclaw/plugin-sdk";
+import { normalizeAccountId } from "openclaw/plugin-sdk";
 
 // Support multiple active clients for multi-account
 const activeClients = new Map<string, MatrixClient>();
@@ -8,7 +8,7 @@ export function setActiveMatrixClient(
   client: MatrixClient | null,
   accountId?: string | null,
 ): void {
-  const key = accountId ?? DEFAULT_ACCOUNT_ID;
+  const key = normalizeAccountId(accountId);
   if (client) {
     activeClients.set(key, client);
   } else {
@@ -17,7 +17,7 @@ export function setActiveMatrixClient(
 }
 
 export function getActiveMatrixClient(accountId?: string | null): MatrixClient | null {
-  const key = accountId ?? DEFAULT_ACCOUNT_ID;
+  const key = normalizeAccountId(accountId);
   return activeClients.get(key) ?? null;
 }
 
diff --git a/extensions/matrix/src/matrix/send/client.ts b/extensions/matrix/src/matrix/send/client.ts
index c1ea1a65b..c1938d4c3 100644
--- a/extensions/matrix/src/matrix/send/client.ts
+++ b/extensions/matrix/src/matrix/send/client.ts
@@ -1,4 +1,5 @@
 import type { MatrixClient } from "@vector-im/matrix-bot-sdk";
+import { normalizeAccountId } from "openclaw/plugin-sdk";
 import type { CoreConfig } from "../../types.js";
 import { getMatrixRuntime } from "../../runtime.js";
 import { getActiveMatrixClient, getAnyActiveMatrixClient } from "../active-client.js";
@@ -19,12 +20,11 @@ export function ensureNodeRuntime() {
 
 export function resolveMediaMaxBytes(accountId?: string): number | undefined {
   const cfg = getCore().config.loadConfig() as CoreConfig;
-  // Check account-specific config first
-  if (accountId) {
-    const accountConfig = cfg.channels?.matrix?.accounts?.[accountId];
-    if (typeof accountConfig?.mediaMaxMb === "number") {
-      return accountConfig.mediaMaxMb * 1024 * 1024;
-    }
+  // Check account-specific config first (normalize to ensure consistent keying)
+  const normalized = normalizeAccountId(accountId);
+  const accountConfig = cfg.channels?.matrix?.accounts?.[normalized];
+  if (typeof accountConfig?.mediaMaxMb === "number") {
+    return accountConfig.mediaMaxMb * 1024 * 1024;
   }
   // Fall back to top-level config
   if (typeof cfg.channels?.matrix?.mediaMaxMb === "number") {