Does FirebaseMessageingService.onMessageReceived need runBlocking when using coroutines?

I need to sync data when a FCM push message is received. My whole infrastructure used coroutines. From the looks of it seems that I need a runBlocking, however I'd best like to avoid that, sync my Syncer exposes only regular functions and uses it's own coroutine scope to run suspend functions

class SomeSyncer {
    private val scope = CoroutineScope ..
    private val _state = MutableFlow...
    val state: Flow<State> get() = _state

    fun sync() {
        scope.launch {
            _state.value = RUNNING
            doSync()
            _state.value = IDLE
        }
    }
}

class FcmService : FirebaseMessageingService {
    override onMessageReceived() {
        someSyncer.sync() ?
        or
        runBlocking {
            someSyncer.sync() ..somehow make it wait? maybe the lowercase coroutineScope?
        }
    }
}

1. Is runBlocking necessary?
2. Can I still run in my custom scope but have the runBlocking work somehow, without refactoring?
3. What if I just use the 1st variant and sideffect to custom scope, will I break wakelocks? (sync is like 1-2seconds max)
4. Or should I expose a suspend function public api (which I don't really want to, it's never needed unless here)