There is no way to delete a topic directly. Not even if you have an app server. That's what I can say after going through the GCM and FCM documents.

The way I understand it, a topic is created when there is at least 1 subscriber and it also gets automatically deleted when there are no more subscribers. So I think the way to do this is to unsubscribe all the subscribers of that topic.

You can check more details on unsubscribing in the Managing Topic Subscriptions on the Server docs (both sites below pretty much says the same thing, but I think it's appropriate to provide a link to both of them):

• https://firebase.google.com/docs/cloud-messaging/topic-messaging#managing_topic_subscriptions_from_the_server
• https://developers.google.com/cloud-messaging/topic-messaging#managing_topic_subscriptions_from_the_server

Hope this helps somehow. Cheers! :)