Not seeing custom payload in Sentry

I'm trying to send custom data with the exception like so:

``` js
Raven.captureException(err, {
  tags: {
    foo: "bar"
  },
  customString: "custom stuff",
  customJSON: {details: 123}
});
```

I can see all of the payload in the ping URL and the event is tagged correctly in Sentry. However, I can't see the customString or customJSON in Sentry 5.4.5. Am I doing something wrong?
