if (this.syncApi instanceof SyncApi)
    // sync V2
    // if the third (`stateAfterEventList`) parameter is undefined, `injectRoomEvents` will use the fourth (`timelineEventList`)
    // parameter with the legacy behaviour (using theimeline events as state events + emitting state changes)
    await this.syncApi.injectRoomEvents(this.room!, [], undefined, [event]);
} else {
    // SSS
    // not used in EC (even though matroska mode supports it) via client `opts.slidingSync`
    await this.syncApi!.injectRoomEvents(this.room!, [], [event]);
}