Most commonly this is because the headphones you are using do not support Apple's head-tracking technology, CoreMotion. See here for a list of headphones that support Dynamic Spatial Audio. If you are using supported headphones, please check the following common issues:

1. Are your headphones connected to your device and is audio playing back through them? Head-tracking requires your headphones to be connected as the primary route where audio is playing back, you can confirm this by tapping the AirPlay button in Portal and seeing whether your headphones display a checkmark next to them.
2. Are your headphones in/on your ears? Head tracking only works when both earpieces are in-place on your head, removing an earpiece or lowering your earphones can pause motion tracking.
3. From time to time, your AirPods may need to be reset. Return them to their case for 10 seconds and re-connect them to your device.
4. Have motion tracking permissions been granted? Portal requires access to your headphones' motion data for Dynamic Spatial Audio to work. You should have been prompted for this when first connecting but you can double check that "Motion & Fitness" is toggled in Settings > Portal.
5. Is your device's software up-to date? We are aware of isolated connectivity issues affecting newer headphone models such as the AirPods Pro (2nd generation), specifically with some iOS & iPadOS 15 versions. We recommend updating to iOS & iPadOS 16 or later if you are able to.
6. Restart your device. Sometimes a little nudge can help reset things and get them back on track.

If you've checked all the above and are still experiencing issues connecting your headphones with Portal, please email us at hello@portal.app