A. Check your iPhone's settings to ensure that vibration is enabled. Go to Settings > Sounds & Haptics and make sure 'Vibrate on Ring' and 'Vibrate on Silent' are turned on. This may help with receiving alerts from the app.
B. If vibration alerts are not supported by the app, consider using a wearable device that can receive notifications from your phone, providing a vibration alert when the app sends an alarm.