Immersive Meditations (Bells, Forest, Music, Storm, and Waves) use something called haptic technology. This technology is used to allow you to feel the vibrations of the meditation through your device. Apple introduced the core haptic technology in their newer devices so you will only find it on the iPhone 8 (running iOS 13) or higher. Unfortunately, this technology does not work on the iPad, iPod touch, iPhone 7 or below, or any Android devices.
To double-check that your haptics are turned on, please follow these directions.