Reload Facebook app after offloading
Make sure you're connected to Wi-Fi
You can only download apps up to 150 MB in size without Wi-Fi. You can also try going on the Internet to check your connection.

If you’re using cellular data or Wi-Fi and have issues with an app, try to connect to another Wi-Fi network. You can use cellular data for apps up to 150 MB* in size.
To check your Wi-Fi connection, try streaming a video from the Internet to see if it loads quickly. Get help connecting to Wi-Fi or contact your Internet provider for more help.

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Pause and restart the app download
Try stopping and restarting the download.
See: How can I cancel an app installation on the iPhone?


Pause the download on the iPhone by tapping the icon.
Connect the iPhone to iTunes. This will cause iTunes to start downloading the app.
Go to the Downloads tab in iTunes and delete the download.


You can also restart your device.