synapse/docs/admin_api/purge_room.md

Purge room API

This API will remove all trace of a room from your database.

All local users must have left the room before it can be removed.

The API is:

POST /_synapse/admin/v1/purge_room

{
    "room_id": "!room:id"
}

You must authenticate using the access token of an admin user.