Unfortunately, there's no way to play sounds unless there's an explicit user interaction. Simply most modern browsers won't allow it (see this entry on Chrome for devs or this thread).

In this case, I'd recommend to ensure that the audio is triggered directly by a user event (the user could trigger the toast by some button interaction); if this is not possible for your application, then an alternative would be to get user permission via a click on a modal or dialog when your application loads.