Please try to force quit Pillow on your device and reopen it. Make sure that your Apple Watch and iPhone are in range and try again.

To force quit Pillow follow these steps:
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​If you have an iPhoneX/iPad 10th generation or newer device:
1. Swipe up from the bottom of the screen to bring up the app switcher.
2. Remove Pillow from the apps that appear by swiping upwards on Pillow's screen.
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​On an iPhone 8/iPad 9th generation or earlier:
​1. Double-click the Home button to show your most recently used apps.
2. Tap on the close button that appears on the top left corner of Pillow.