get https://api.onesignal.com/apps//users/by//
Retrieve a user including aliases, properties, and subscriptions.
Overview
Use this API to lookup a user's properties, identity, and subscription details.
For details, see Users, Subscriptions, and Aliases.
How to use this API
In most cases, you will use your external_id as the alias_label and the value of that ID in the alias_id. You an also use custom Aliases but we highly recommend setting the external_id as your main user ID.
To look up a user via OneSignal ID, use onesignal_id as the alias_label. Note: Authentication using any alias other than the OneSignal ID is required.