Stephen, I have tried all you have suggested, many times, and have even reset the phone to factory settings. The app definitely does not pop up a notification when the phone screen is asleep, wake the screen and notifications come through.
All my settings are correct both for the phone and app.
Can you confirm that your notifications come through when your phone screen is both asleep and awake ?
The smart watering has the controller to water at 3.00pm today 1st May ( Australia). If it does water, we had 1mm of rain this morning, I will report here with the outcome.