I cannot feel any vibration

Work through these in order.

1. Check what you are playing. Sounds do not vibrate the transducers on their own. Open the Generator and start an actual frequency.
2. Check placement. The pads must sit on your cheekbones, on bone, just in front of your ears. On the ear or on soft tissue kills the vibration.
3. Check contact. Thick hair, a hat, or glasses arms between the pad and your skin dampen it.
4. Raise the volume slowly. Vibration intensity scales with volume.
5. Try a lower frequency. Low frequencies vibrate far more noticeably than high ones. If you were on a 528 Hz tone, try delta or theta and compare.
6. Confirm the audio is routing to the headphones, not your phone speaker. Check the output selector on the player screen.