Nginx rejects request bodies larger than 1 MB by default, returning 413 Request Entity Too Large before the request ever reaches your app. Raise the limit to whatever you actually want to allow.

Site-wide (in http { } or a server { }):

client_max_body_size 100m;

Or just on the upload endpoint, keeping the rest tight:

location /upload {
    client_max_body_size 500m;
    proxy_pass http://127.0.0.1:3000;

    # Big uploads can take a while — don't time out mid-transfer.
    proxy_request_buffering off;   # stream to the backend instead of buffering whole body to disk
    proxy_read_timeout  300s;
    proxy_send_timeout  300s;
}

Details:

client_max_body_size 0; disables the check entirely (unlimited) — usually a bad idea; pick a real ceiling.
The directive is inherited, so set it at http for a global default and override per location for upload paths.
413 still appearing after raising it? Check you edited the server block that actually handles the request, and reload (not just nginx -t). If a separate reverse proxy or CDN sits in front, raise its limit too.
For streaming large files to a backend, proxy_request_buffering off; avoids buffering the entire body to a temp file first. For PHP-FPM, also raise upload_max_filesize and post_max_size in php.ini.

sudo nginx -t && sudo nginx -s reload

Raise the upload size limit (fix 413)