## The symptom
After upgrading react-calendly to v3, the `onEventScheduled` callback on
`CalendlyEventListener` stops firing. The iframe src URL contains pageSettings
colors with a leading `#`, e.g. `background_color=#fff`. Calendly redirects that
URL and drops the `embed_domain` query parameter in the process. Without
`embed_domain` the iframe cannot post messages back, so no events are received.
Downgrading to 2.1.0 (where `embed_domain` was set differently) masked it.
## The fix
Remove the `#` from all pageSettings color values. Use `"ffffff"` instead of
`"#ffffff"` for `backgroundColor`, `primaryColor`, and `textColor`:
```js
pageSettings: {
backgroundColor: 'ffffff',
primaryColor: '00a2ff',
textColor: '4d5055'
}
```
The reporter confirmed this fixed it.
## How to spot it
Open the rendered iframe src in devtools. If the `embed_domain` query parameter
is missing from the final URL, events cannot flow. Anything that mangles the
embed URL (like the `#`) breaks event delivery silently: the widget looks fine,
it just never calls back.