An update is required to use cellular data on this iphone

Hello,

This has happened to me previously as well, here are some steps you can take to fix this:

If we understand your post correctly, you're seeing an error message that an update is required to use cellular data on this phone. We're happy to help!

Support step 1:

It sounds like there is a carrier update that is required to use cellular data.

"Carrier settings updates let your carrier provider update carrier network and related settings to improve cellular network connectivity and performance. Carrier settings updates can also add support for new features like 5G or Wi-Fi Calling.

When a carrier settings update is available, you'll be prompted to install it. Installation takes less than one minute, and you can keep using your device normally. If your carrier releases a mandatory update, you'll see an OK button instead of an Update button to let you know that the update was downloaded and installed.

If you dismiss the installation notification, you can manually update carrier settings by following these steps:

1. Make sure that your device is connected to Wi-Fi or a cellular network.
2. Tap Settings > General > About.
3. Follow the onscreen instructions to install your carrier update.

If you set up a new eSIM or insert a new SIM card into your iPhone or iPad, you might need to download the carrier settings for your new carrier.

To see the version of carrier settings on your device, tap Settings > General > About and look next to Carrier. To see additional carrier information, tap the version number. To verify that you have the latest carrier settings installed, contact your carrier."

Manually update your carrier settings on your iPhone or iPad

For the messages that you're not receiving, does this happen on Wi-Fi as well as cellular data?

If it is only on cellular data then when your carrier updates are installed that issue should be resolved. If this is also happening on Wi-Fi then following the steps in the article below.

If you can't send or receive messages on your iPhone or iPad

Support Step 2:

Updating your device: Update your iPhone or iPad – Apple Support (AU)

Support Step 3:

Get further support from Apple Support

Let us know if you have any questions.

Thank you for using Apple Support Communities.

Take care!

This may help --> Cellular Update Failed No Service Signal … - Apple Community