This error running cakephp 3 behind a nginx proxy on port 80 and proxying back to a docker container published on port 8080. Got this error message when clicking on the DebugKit toolbar

toolbar-app.js:31 Failed to execute 'postMessage' on 'DOMWindow': The target origin provided ('http://php-docker.local:8080') does not match the recipient window's origin ('http://php-docker.local').

The fix was to set the correct host header

server {

        listen 80;
        server_name php-docker.local;
        # add proxy_set_header
        proxy_set_header Host $host;

        location / {
                proxy_pass http://php-docker.local:8080/;
        }

}