diff --git a/examples/graph/src/index.ts b/examples/graph/src/index.ts
index 5588c2fab..274b19b3f 100644
--- a/examples/graph/src/index.ts
+++ b/examples/graph/src/index.ts
@@ -10,6 +10,8 @@ const app = new App({
      */
     defaultConnectionName: 'graph'
   },
+  // Instead of setting in ConsoleLogger like below, you can also 
+  // set LOG_LEVEL=debug or LOG_LEVEL=trace env var for verbose SDK logging
   logger: new ConsoleLogger('@tests/auth', { level: 'debug' }),
     // This is an example of overriding the token URL for a specific region (e.g., Europe).
     // Uncomment this block if needed.
@@ -43,4 +45,10 @@ app.event('signin', async ({ send, userGraph, token }) => {
   await send(`user "${me.displayName}" signed in. Here's the token: ${JSON.stringify(token)}`);
 });
 
+app.on('signin.failure', async ({ activity, log, send }) => {
+  const { code, message } = activity.value;
+  log.error(`sign-in failed: ${code} - ${message}`);
+  await send('sign-in failed. please contact your admin.');
+});
+
 app.start().catch(console.error);
diff --git a/packages/apps/src/app.oauth.ts b/packages/apps/src/app.oauth.ts
index ca525a31f..b5bd3189c 100644
--- a/packages/apps/src/app.oauth.ts
+++ b/packages/apps/src/app.oauth.ts
@@ -1,6 +1,7 @@
 import { AxiosError } from 'axios';
 
 import {
+  ISignInFailureInvokeActivity,
   ISignInTokenExchangeInvokeActivity,
   ISignInVerifyStateInvokeActivity,
   TokenExchangeInvokeResponse,
@@ -103,3 +104,47 @@ export async function onVerifyState<TPlugin extends IPlugin>(
     return { status: 412 };
   }
 }
+
+/**
+ * Default handler for signin/failure invoke activities.
+ *
+ * Teams sends a signin/failure invoke when SSO token exchange fails
+ * (e.g., due to a misconfigured Entra app registration). This handler
+ * logs the failure details and emits an error event so developers are
+ * notified rather than having the failure silently swallowed.
+ *
+ * Known failure codes (sent by the Teams client):
+ * - `installappfailed`: Failed to install the app in the user's personal scope (non-silent).
+ * - `authrequestfailed`: The SSO auth request failed after app installation (non-silent).
+ * - `installedappnotfound`: The bot app is not installed for the user or group chat.
+ * - `invokeerror`: A generic error occurred during the SSO invoke flow.
+ * - `resourcematchfailed`: The token exchange resource URI on the OAuthCard does not
+ *   match the Application ID URI in the Entra app registration's "Expose an API" section.
+ * - `oauthcardnotvalid`: The bot's OAuthCard could not be parsed.
+ * - `tokenmissing`: AAD token acquisition failed.
+ * - `userconsentrequired`: The user needs to consent (handled via OAuth card fallback,
+ *   does not typically reach the bot).
+ * - `interactionrequired`: User interaction is required (handled via OAuth card fallback,
+ *   does not typically reach the bot).
+ */
+export async function onSignInFailure<TPlugin extends IPlugin>(
+  this: App<TPlugin>,
+  ctx: contexts.IActivityContext<ISignInFailureInvokeActivity, PluginAdditionalContext<TPlugin>>
+) {
+  const { log, activity, next } = ctx;
+  const { code, message } = activity.value;
+
+  log.warn(
+    `sign-in failed for user "${activity.from.id}" in conversation "${activity.conversation.id}": ${code} — ${message}. ` +
+    'If the code is \'resourcematchfailed\', verify that your Entra app registration has \'Expose an API\' configured ' +
+    'with the correct Application ID URI matching your OAuth connection\'s Token Exchange URL.'
+  );
+
+  this.events.emit('error', {
+    error: new Error(`Sign-in failure: ${code} — ${message}`),
+    activity,
+  });
+
+  next(ctx);
+  return { status: 200 };
+}
diff --git a/packages/apps/src/app.process.spec.ts b/packages/apps/src/app.process.spec.ts
index 215cc2ea5..f63e8d4f5 100644
--- a/packages/apps/src/app.process.spec.ts
+++ b/packages/apps/src/app.process.spec.ts
@@ -1,4 +1,4 @@
-import { IMessageActivity, InvokeResponse, ITaskFetchInvokeActivity, IToken, MessageActivity, TaskModuleResponse } from '@microsoft/teams.api';
+import { IMessageActivity, InvokeResponse, ISignInFailureInvokeActivity, ITaskFetchInvokeActivity, IToken, MessageActivity, TaskModuleResponse } from '@microsoft/teams.api';
 
 import { App } from './app';
 import { IActivityEvent } from './events/activity';
@@ -108,5 +108,29 @@ describe('App', () => {
       expect(response.status).toBe(500);
       expect(response.body).toBeUndefined();
     });
+
+    it('should handle signin/failure invoke with default handler', async () => {
+      const signinFailureActivity = {
+        type: 'invoke',
+        name: 'signin/failure',
+        channelId: 'msteams',
+        from: { id: 'user-1', name: 'Test User' },
+        conversation: { id: 'conv-1' },
+        recipient: { id: 'bot-1', name: 'Test Bot' },
+        value: {
+          code: 'resourcematchfailed',
+          message: 'Resource match failed',
+        },
+      } as unknown as ISignInFailureInvokeActivity;
+
+      const event: IActivityEvent = {
+        token: token,
+        activity: signinFailureActivity,
+        sender: senderPlugin,
+      };
+
+      const response = await app.process(senderPlugin, event);
+      expect(response.status).toBe(200);
+    });
   });
 });
diff --git a/packages/apps/src/app.ts b/packages/apps/src/app.ts
index 4a71efd74..e023b0861 100644
--- a/packages/apps/src/app.ts
+++ b/packages/apps/src/app.ts
@@ -27,8 +27,9 @@ import {
   onError,
 } from './app.events';
 import {
+  onSignInFailure,
   onTokenExchange,
-  onVerifyState
+  onVerifyState,
 } from './app.oauth';
 import { getMetadata, getPlugin, inject, plugin } from './app.plugins';
 import { $process } from './app.process';
@@ -347,6 +348,13 @@ export class App<TPlugin extends IPlugin = IPlugin> {
       callback: ctx => this.onVerifyState(ctx),
     });
 
+    this.router.register({
+      name: 'signin.failure',
+      type: 'system',
+      select: activity => activity.type === 'invoke' && activity.name === 'signin/failure',
+      callback: ctx => this.onSignInFailure(ctx),
+    });
+
     this.event('error', ({ error }) => {
       this.log.error(error.message);
 
@@ -518,6 +526,7 @@ export class App<TPlugin extends IPlugin = IPlugin> {
 
   protected onTokenExchange = onTokenExchange; // eslint-disable-line @typescript-eslint/member-ordering
   protected onVerifyState = onVerifyState; // eslint-disable-line @typescript-eslint/member-ordering
+  protected onSignInFailure = onSignInFailure; // eslint-disable-line @typescript-eslint/member-ordering
 
   ///
   /// Events
diff --git a/packages/cli/templates/typescript/graph/src/index.ts b/packages/cli/templates/typescript/graph/src/index.ts
index 67ff5c281..1ab188211 100644
--- a/packages/cli/templates/typescript/graph/src/index.ts
+++ b/packages/cli/templates/typescript/graph/src/index.ts
@@ -42,4 +42,10 @@ app.event('signin', async ({ send, userGraph }) => {
   );
 });
 
+app.on('signin.failure', async ({ activity, log, send }) => {
+  const { code, message } = activity.value;
+  log.error(`sign-in failed: ${code} - ${message}`);
+  await send('sign-in failed. please contact your admin.');
+});
+
 app.start(process.env.PORT || 3978).catch(console.error);