Update required to use cellular data

In addition to what the others said, you might also try:

Update your carrier settings on your iPhone or iPad - Apple Support

If Settings > Cellular shows the update error check https://support.apple.com/iphone-7-no-service

Do the steps in:

If you see an Update Failed or Apple Pay Not Available alert after iOS update or restart - Apple Support

If the issue persists it's likely the iPhone will need service:

Contact Apple for support and service - Apple Support

Good luck!

Golfman1160 Said:

"Update required to use cellular data"

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What is the Update?

What exactly is the update our are trying to install? If it requires cellular data, I am not so certain as to why they would restrict you on that(a scam perhaps?).

Contact the Developer:

So, if not Apple, then contact the Developer, asking them for a link where you can go and get the update from. Once you get the link, download it using WiFi.

Important:

Backup First: Make a backup of your device using iCloud or your computer, that ware you can have something to restore your iPhone from, should anything go wrong, after the update installation.