What’s Linked wallpaper? How to use it?

“The Linked Wallpaper is a wonderful feature which can let your friend sync wallpaper settings with you.To use Linked wallpaper, please:
1. Select a wallpaper;

2. Tap on “Set for us”;
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3. Log-in to your Facebook or Google+ account;
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4. Input APUS ID of your friend

5. Your friend will receive a notification after establishing the connection. Wait your friend to approve the request.”