diff --git a/changelog.md b/changelog.md
index f109db9..4aa59ab 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,5 +1,14 @@
 # Changelog
 
+## 2025-07-22 - 3.1.1 - fix(oauth)
+Fix OAuth token authentication flow for existing installations
+
+- Fixed initWithExistingInstallation to properly create new sessions with existing installation/device
+- OAuth tokens now correctly skip installation/device steps when they already exist
+- Session creation still uses OAuth token as the secret parameter
+- Properly handles "Superfluous authentication" errors by reusing existing installation
+- Renamed initWithExistingSession to initWithExistingInstallation for clarity
+
 ## 2025-07-22 - 3.1.0 - feat(oauth)
 Add OAuth session caching to prevent multiple authentication attempts
 
diff --git a/package.json b/package.json
index 92195bf..2d934b3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@apiclient.xyz/bunq",
-  "version": "3.1.0",
+  "version": "3.1.1",
   "private": false,
   "description": "A full-featured TypeScript/JavaScript client for the bunq API",
   "type": "module",
diff --git a/ts/bunq.classes.account.ts b/ts/bunq.classes.account.ts
index ad40305..ad7c698 100644
--- a/ts/bunq.classes.account.ts
+++ b/ts/bunq.classes.account.ts
@@ -64,10 +64,10 @@ export class BunqAccount {
             const errorMessages = error.errors.map(e => e.error_description).join(' ');
             if (errorMessages.includes('Superfluous authentication') ||
                 errorMessages.includes('Authentication token already has a user session')) {
-              console.log('OAuth token already has an active session, attempting to reuse...');
-              // Try to use the token directly without creating new session
-              await this.apiContext.initWithExistingSession();
-              // Cache the context with existing session
+              console.log('OAuth token already has installation/device, attempting to create new session...');
+              // Try to create a new session with existing installation/device
+              await this.apiContext.initWithExistingInstallation();
+              // Cache the context with new session
               BunqAccount.oauthSessionCache.set(cacheKey, this.apiContext);
             } else {
               throw error;
diff --git a/ts/bunq.classes.apicontext.ts b/ts/bunq.classes.apicontext.ts
index 205a8eb..66eb78d 100644
--- a/ts/bunq.classes.apicontext.ts
+++ b/ts/bunq.classes.apicontext.ts
@@ -171,31 +171,49 @@ export class BunqApiContext {
   }
 
   /**
-   * Initialize with existing OAuth session (skip installation/device/session creation)
+   * Initialize with existing installation and device (for OAuth tokens that already completed these steps)
    */
-  public async initWithExistingSession(): Promise<void> {
-    // For OAuth tokens that already have a session, we just need to:
-    // 1. Use the OAuth token as the session token
-    // 2. Set OAuth mode for proper expiry handling
+  public async initWithExistingInstallation(): Promise<void> {
+    // For OAuth tokens that already have installation/device but need a new session
+    // We need to:
+    // 1. Try to load existing installation/device info
+    // 2. Create a new session using the OAuth token as the secret
     
-    this.context.sessionToken = this.options.apiKey;
+    const existingContext = await this.loadContext();
     
-    // Create session instance with existing token
-    this.session = new BunqSession(this.crypto, this.context);
-    this.session.setOAuthMode(true);
-    
-    // Try to get user info to validate the session
-    try {
-      // This will test if the session is valid
-      const testClient = this.session.getHttpClient();
-      const response = await testClient.get('/v1/user');
+    if (existingContext && existingContext.clientPrivateKey && existingContext.clientPublicKey) {
+      // Restore crypto keys from previous installation
+      this.crypto.setKeys(
+        existingContext.clientPrivateKey,
+        existingContext.clientPublicKey
+      );
       
-      if (response && response.Response) {
-        console.log('Successfully reused existing OAuth session');
+      // Update context with existing installation data
+      this.context = { ...this.context, ...existingContext };
+      
+      // Create new session instance
+      this.session = new BunqSession(this.crypto, this.context);
+      
+      // Try to create a new session with the OAuth token
+      try {
+        await this.session.init(
+          this.options.deviceDescription,
+          this.options.permittedIps || [],
+          true // skipInstallationAndDevice = true
+        );
+        
+        if (this.options.isOAuthToken) {
+          this.session.setOAuthMode(true);
+        }
+        
         await this.saveContext();
+        console.log('Successfully created new session with existing installation');
+      } catch (error) {
+        throw new Error(`Failed to create session with OAuth token: ${error.message}`);
       }
-    } catch (error) {
-      throw new Error(`Failed to reuse OAuth session: ${error.message}`);
+    } else {
+      // No existing installation, fall back to full init
+      throw new Error('No existing installation found, full initialization required');
     }
   }
 }
\ No newline at end of file
diff --git a/ts/bunq.classes.session.ts b/ts/bunq.classes.session.ts
index d069b48..e35cc95 100644
--- a/ts/bunq.classes.session.ts
+++ b/ts/bunq.classes.session.ts
@@ -24,14 +24,16 @@ export class BunqSession {
   /**
    * Initialize a new bunq API session
    */
-  public async init(deviceDescription: string, permittedIps: string[] = []): Promise<void> {
-    // Step 1: Installation
-    await this.createInstallation();
+  public async init(deviceDescription: string, permittedIps: string[] = [], skipInstallationAndDevice: boolean = false): Promise<void> {
+    if (!skipInstallationAndDevice) {
+      // Step 1: Installation
+      await this.createInstallation();
+      
+      // Step 2: Device registration
+      await this.registerDevice(deviceDescription, permittedIps);
+    }
     
-    // Step 2: Device registration
-    await this.registerDevice(deviceDescription, permittedIps);
-    
-    // Step 3: Session creation
+    // Step 3: Session creation (always required)
     await this.createSession();
   }