OneSignal external_user_id and multiple devices for the same user

Question

I'm using OneSignal as notification platform in my Spring Boot application.

I want to send the very same push notification for each device of a user and I'm trying to understand if the external_user_id can be setted multiple times.

I don't want to save into my DB different "player_id" (device ID) for the same user so I'm trying to figure out if I can user the external_user_id as a "tag" to indentify all user's devices.

I mean:

User A open the Mobile app with his First device and register a custom external_user_id into OneSignal
User A open the Mobile app with his Second device and register the same external_user_id into OneSignal.

I send a push notification calling OneSignal API from my Spring Boot application using this external_user_id so the User A will receive the very same notification on both his devices.

Is is possibile or external_user_id must be unique?

Thanks.

user_3335046 · Answer

This is how it should be done.

One user has the same external_user_id on all their devices, his is unique to them eg their email.
The Server Rest API is used for sending messages to a single user on multiple devices.

Look at these links for details.

Create a notification
transactional messages
User to user messages

OneSignal external_user_id and multiple devices for the same user

1 Answers