Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

This error occurs when you are trying to send HTTP headers to the client (i.e. the user's browser) after they have already been sent. Once the headers have been sent, they cannot be modified or sent again.

This error typically occurs when there is a logic error in your code, such as sending headers in a loop or sending headers after the response has already been sent.

To fix this error, you will need to carefully review your code and ensure that you are only sending headers once, and that they are being sent before any response data is sent. You may also need to refactor your code to ensure that headers are only being sent in the appropriate places.

Here are a few tips to help you avoid this error:

1. Make sure that you are not sending headers in a loop or conditional statement that may be executed multiple times.

2. If you are using middleware or other third-party libraries, make sure that they are not sending headers after the response has already been sent.

3. Use a tool like Postman or a browser extension like Live HTTP Headers to inspect the headers that are being sent and received, and look for any anomalies that may be causing the error.

4. If you are still having trouble, try using a debugger to step through your code and identify where the headers are being sent and why they may be causing an error.