Hello,

I found and fixed a bug in the mern-netflix-app branch where the backend was throwing an error due to a syntactical bug.

Problem

The backend is throwing ERR_HTTP_HEADERS_SENT errors when JWT token validation failed

Root Cause

The error occurs because your code is trying to send multiple responses for a single request due to a missing return keyword. Because of this missing return keyword, when a response error (403, "Token is invalid") is received, the route handler tries to send another response because it moves on to next().

Solution

Add return keyword:

• BUGGY: if (err) res.status(403).json("Token is not valid!");
• FIXED: if (err) return res.status(403).json("Token is not valid!");

Files Affected

• routes/movies.js (line 83)
• routes/lists.js (line 57)
• All routes using the JWT verification middleware

Testing

• verify that invalid tokens return proper 403 responses without server errors
• check that multiple concurrent requests don't cause header conflicts

Notes

This fix does not change any database or frontend behavior; it only ensures the server handles responses correctly.

Have a good day,
Anna