Firebase Web Push Custom Chrome Badge

This topic is well covered on Android and iOS (ANCS) however it is not discussed in any documentation for Web notifications.

My goals is to create a custom Chrome notification badge for mobile (see image below). I would have thought it was as simple as setting a field in web.manifest.json or in the payload sent to FCM but these have no effect.

I found some interesting discussion around a badge and purpose field for web manifest here - https://github.com/w3c/manifest/issues/480 but does not appear to be in use by Chrome.