Follow the below steps to configure OneSignal for sending push notifications:

1. Go to https://onesignal.com and create an account.

2. In the dashboard, click on Add a new app. You will see the following dialog:

3. Fill it with the name that you want and click on Create. It will open the following dialog:

4. Select Apple iOS and Hit Next. You will see the following:

5. Select Upload optional sandbox certificate and upload ...