Batch offers two solutions in case you need to target specific user IDs:
Send real-time notifications using the Transactional API
The Transactional API is made for 1-to-1 or 1-to-few interactions. It allows you to send push notifications to a specific list of IDs (push tokens, Advertising IDs or Custom User IDs) based on events in your back-end.
Use it to send action-oriented or time-sensitive push notifications.
- Action-oriented notifications: New message, friend request, reached credit limit, user's turn in a game, etc.
- Time-sentitive notifications: Delivered order, delayed flight, canceled train, etc.
You will find more information on the Transactional API here: https://batch.com/doc/api/transactional.html
Create and target segments using Batch's Custom Audiences
Custom audiences allow you upload static segments exported from your userbase (e.g. top 500 buyers, etc) or created by third-party tools. You can easily retarget these custom audiences with a push or an In-App campaign from the dashboard.
You can easily create a custom audience by uploading a .txt or .csv file from the dashboard settings > "Audiences" tab:
You can also create and update audiences remotely, using the Custom Audience API.