delete https://api.onesignal.com/apps//users/by//
Delete a user including all associated properties, subscriptions, and identity.
Overview
This API deletes the user, along with all associated subscriptions, properties, and aliases. The deletion is performed asynchronously.
How to use this API
You must be able to identify the user. The most common way to do this is with your external_id but the onesignal_id or custom Aliases can work as well.