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# Troubleshoot 502 Bad Gateway

## Problem

 I'm using nginx and the error log is showing the following message:

```

[error] 6890#0: *15355 upstream sent too big header while reading response header from upstream,
    client: 203.0.113.2, server: subdomain.example.com,
    request: "POST /en/install/step4 HTTP/2.0",
    upstream: "https://subdomain.example.com:7081/en/install/step4",
    host: "subdomain.example.com",
    referrer: "https://subdomain.example.com/en/install/step3"

```

## Cause

A request cannot be processed by the proxy server because of insufficient buffer size.

## Resolution

  **Plesk**  
 If using Plesk, see: <https://support.plesk.com/hc/en-us/articles/12377655871767-Plesk-site-unavailable-502-Bad-Gateway-upstream-sent-too-big-header-while-reading-response-header>

To increase the buffer size follow the steps below:

1. Increase 'buffers" and 'buffer\_size' in `/etc/nginx/nginx.conf `under `http { `section. For example:  
    `proxy_buffers 8 16k;<br></br>proxy_buffer_size 32k;<br></br>fastcgi_buffers 8 16k;<br></br>fastcgi_buffer_size 32k;`
2. Restart `nginx` service