Can’t access cellular data

Your screen shot suggests that in order to access cellular data on your iPhone, an update is required. This means that an update other than an iOS version update.

What SravanKrA suggested is to see whether you have a carrier update available and to check it - Open Settings ➔ Genearal ➔ About : Stay on this screen for 5 seconds and SEE whether a window pops up to make a carrier update.. Note that this window only pops up IF there is a carrier update available. If there is a pop up offering an update then take it and update the carrier settings.

Axel F.

Few Carrier (Cellular Service Provider) do not provide Carrier Settings in full but they offer APN settings for example

• Google FI which has APN to be entered manually as h2g2
• BSNL in India which provides APN pin to be updated manually as bsnlnet

Settings > Mobile Data > APN [under Mobile Data APN] enter the APN pin

Use the APN pin based on your carrier. Ask them or google and search.

If you do see the option to enter APN then the only option is give below

Carrier Update (Required): Released by your Cellular Service provider (Carrier Update), affects your Outgoing / Incoming calls, SMS, Data etc..

How to Update Carrier Settings

You can manually check for and install a carrier settings update with these steps: Make sure your device is connected to a Wi-Fi or cellular network. Tap Settings > General > About. If an update is available, you'll see an option to update your carrier settings.

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