Hey Luke! In a push notification, you can specify a title and a body message.

Check out steps 4 & 5 in this help article on creating a push notification message: https://customer.io/docs/send-push/#create-a-push-notification. :) 

Additonally I found this:

Android

It is possible to use HTML tags in Android notifications. So you can try to use <br> (Source).

iOS

You can try using an escape here. I am not sure if this is possible in “simple push” so you migh have to change to “custom payload“ (Source).

Hope that helps,

Felix