If you find that you're not receiving notifications for Sideline, make sure you have notifications turned on!
You can find this setting in the Sideline app.
1. Tap the Sideline icon to access your Settings
2. Scroll down and make sure Show Message Preview is on, or Email Notifications if you'd like to have your messages sent to your email as well
If you're not receiving notifications after enabling these options, you may need to check your device's settings for Sideline to ensure you've allowed notifications