New content and updates are regularly being released for Pokémon Sleep. Read on below to learn more:

Announcement Regarding Account Linking

Thank you for playing Pokémon Sleep!

We recommend linking your account, so that your data is not lost if you change devices or delete the app.
Please try applying the following settings.

1. From the home screen, tap Main Menu > Settings and More > Link Accounts
2. Select the service you’d like to link with
3. Follow the on-screen instructions to link

Or, if you instead select Issue a Transfer Code, please try the following after step 1 above.
2. Follow the on-screen instructions to issue the code
3. Tap Take Screenshot (optional)

We hope you continue to enjoy Pokémon Sleep!

Source: Official Pokémon Sleep news