Debugging Expo Connectivity & Authentication

This skill outlines a systematic approach to resolving common connectivity and authentication blockers when developing React Native (Expo) apps on Windows, interacting with a local backend.

1. Authentication: 401 Unauthorized Loops

Symptom:

• Infinite loading spinners or repeated blocking errors when trying to save data.
• API calls return 401 Unauthorized regardless of login state.

Root Cause:

• Stale or invalid JWT tokens persisted on the device (e.g., from a previous auth implementation).
• App continues sending the bad token without clearing it, leading to a loop.

Resolution:

• Implement Auto-Logout: Add an Axios response interceptor to catch 401 errors globally.