NestJS Swagger UI loads on real Android device but "Try it out" fails with CORS / Failed to fetch

I am developing a NestJS backend and testing it on a real Android device.

The Setup:

• Backend IP: 192.168.1.5:3000 (MacBook)

• Device: Real Android phone connected to the same Wi-Fi.

• Observation: I can successfully open the Swagger documentation in the phone's browser at http://192.168.1.5:3000/api/docs.

The Problem: When I click "Try it out" for any endpoint (e.g., /auth/login) inside the Swagger UI on the phone, the request fails with the following message:

TypeError: Failed to fetch Possible reasons: CORS, Network failure, or URL scheme must be http or https

It works perfectly on the Android Emulator using http://10.0.2.2:3000.

Current main.ts CORS config:

app.enableCors({
  origin: ['http://localhost:5175'], // My Vite frontend
  methods: ['GET', 'POST', 'PUT', 'DELETE', 'OPTIONS', 'PATCH'],
  allowedHeaders: ['Content-Type', 'Authorization'],
  credentials: true,
});

await app.listen(3000, '0.0.0.0');
 

2. Returning Subclasses

A factory constructor can decide which specific implementation to return based on the arguments provided. This is often used in the Factory Pattern.

app.enableCors({
  origin: ['http://localhost:5175'], // My Vite frontend
  methods: ['GET', 'POST', 'PUT', 'DELETE', 'OPTIONS', 'PATCH'],
  allowedHeaders: ['Content-Type', 'Authorization'],
  credentials: true,
});

await app.listen(3000, '0.0.0.0');

Current Swagger Config:

const swaggerConfig = new DocumentBuilder()
  .setTitle('Liaison360 API')
  .addServer('http://localhost:3000', 'Local Development')
  .addServer('http://192.168.1.5:3000', 'Local Network')
  .build();


What I've tried:

1. Verified the phone and laptop are on the same network.

2. Verified the backend is listening on 0.0.0.0.

3. Since the Swagger HTML page loads, I know the port is not blocked by a firewall.

Why does the browser allow loading the Swagger page but block the actual API fetch requests, and how should I configure CORS in NestJS to allow this testing?