Hi. It is a very nice post for those you want to invest time and configure OneSignal by themselves from scratch. I did it too few years ago and found this process too time consuming.
With this though me and my team invested hundreds of development and testing hours to save others a headache with OneSignal. As a result, we recenlty launched “OneSignal MAX Push Notifications (iOS + Android + Web)” plugin.
In the following post I tell more about the features of this plugin: [NEW Plugin] OneSignal MAX Push Notifications (iOS + Android + Web)