API Connectivity Failure: Device-Specific Timeout on Railway-Hosted Spring Boot App

Question

### **Key Information**

**Category Details**  
**Environment -** Spring Boot app hosted on Railway.  
**Affected Device -** One testing laptop and testing mobile (works with VPN, times out without it).  
**Other Devices -** API works on other machines/networks.**Error**`Connection Timed Out` (e.g., `ERR_CONNECTION_TIMED_OUT` or `HTTP 504`).  
**Pattern -** VPN usage resolves the issue on the problematic device.

**Error Analysis ("Central Station" Perspective)**

**1\. Railway Logs & Metrics**

* **Observation**:  
   * No errors in server logs for requests from the affected device (indicates the request never reached Railway).  
   * Successful requests from other devices/VPN IPs are logged.
* **Conclusion**:  
The timeout occurs **before** the request reaches Railway’s servers (client-side or network-layer issue).