External POST request no payload

I’m having a similar problem to this:

I have a discourse installation running on forum.mydomain.com. I set up a webhook to register user events and have verified it works using RequestBin. However, my receive action only receives headers, but no body. I have disabled csrfvalidation and there is no https redirect.

I also have a mailchimp webhook, and I’m handling that post request nearly identically, and it works just fine. That makes me think it has something to do with the request coming from a subdomain.

    public function beforeAction($action)
    {
        if (in_array($action->id, ['forum-receive'])) {
            $this->enableCsrfValidation = false;
        }
        return parent::beforeAction($action);
    }
    public function actionForumReceive()
    {
        Yii::$app->response->format = Response::FORMAT_JSON;
        $request = Yii::$app->request;
        $headers = $request->headers;
        if ($headers->has('X-Discourse-Event')
            && $event = $headers->get('X-Discourse-Event')) {

            if ($event === 'user_created') {
                file_put_contents('discourse.txt', print_r($request, true), FILE_APPEND);
                return ['type' => 'new user'];
            }
        }
        throw new NotFoundHttpException;
    }

The action returns a response with status 200 and “new user”, but the body is empty. The apache log shows the request was received, but nothing noteworthy. I’m at a loss of what else to look at.

Here is discourse.txt. I’m not sure why, but it says csrfvalidation is still enabled.

    yii\web\Request Object
    (
    [enableCsrfValidation] => 1
    [csrfParam] => _csrf-frontend
    [csrfCookie] => Array
        (
            [httpOnly] => 1
        )

    [enableCsrfCookie] => 1
    [enableCookieValidation] => 1
    [cookieValidationKey] => zZjHj-Bo1L48qe3Z-yXF437Ym77KTe78l
    [methodParam] => _method
    [parsers] => Array
        (
        )

    [trustedHosts] => Array
        (
        )

    [secureHeaders] => Array
        (
            [0] => X-Forwarded-For
            [1] => X-Forwarded-Host
            [2] => X-Forwarded-Proto
            [3] => Front-End-Https
            [4] => X-Rewrite-Url
        )

    [ipHeaders] => Array
        (
            [0] => X-Forwarded-For
        )

    [secureProtocolHeaders] => Array
        (
            [X-Forwarded-Proto] => Array
                (
                    [0] => https
                )

            [Front-End-Https] => Array
                (
                    [0] => on
                )

        )

    [_cookies:yii\web\Request:private] => 
    [_headers:yii\web\Request:private] => yii\web\HeaderCollection Object
        (
            [_headers:yii\web\HeaderCollection:private] => Array
                (
                    [x-discourse-event] => Array
                        (
                            [0] => user_created
                        )

                    [x-discourse-event-type] => Array
                        (
                            [0] => user
                        )

                    [x-discourse-event-id] => Array
                        (
                            [0] => 19
                        )

                    [x-discourse-instance] => Array
                        (
                            [0] => https://forum.mydomain.com
                        )

                    [content-type] => Array
                        (
                            [0] => application/json
                        )

                    [accept] => Array
                        (
                            [0] => */*
                        )

                    [user-agent] => Array
                        (
                            [0] => Discourse/2.4.0.beta10
                        )

                    [content-length] => Array
                        (
                            [0] => 3936
                        )

                    [connection] => Array
                        (
                            [0] => close
                        )

                    [x-accel-internal] => Array
                        (
                            [0] => /internal-nginx-static-location
                        )

                    [x-real-ip] => Array
                        (
                            [0] => 172.17.0.2
                        )

                    [host] => Array
                        (
                            [0] => mydomain.com
                        )

                )

        )

    [_rawBody:yii\web\Request:private] => 
    [_bodyParams:yii\web\Request:private] => 
    [_queryParams:yii\web\Request:private] => 
    [_hostInfo:yii\web\Request:private] => 
    [_hostName:yii\web\Request:private] => 
    [_baseUrl:yii\web\Request:private] => 
    [_scriptUrl:yii\web\Request:private] => /index.php
    [_scriptFile:yii\web\Request:private] => 
    [_pathInfo:yii\web\Request:private] => forum-receive
    [_url:yii\web\Request:private] => /forum-receive
    [_port:yii\web\Request:private] => 
    [_securePort:yii\web\Request:private] => 
    [_contentTypes:yii\web\Request:private] => 
    [_languages:yii\web\Request:private] => 
    [_csrfToken:yii\web\Request:private] => 
    [_isConsoleRequest:yii\base\Request:private] => 
    [_events:yii\base\Component:private] => Array
        (
        )

    [_eventWildcards:yii\base\Component:private] => Array
        (
        )

    [_behaviors:yii\base\Component:private] => 
    [_scriptFile:yii\base\Request:private] => 
)