Data Issues

Make sure that cellular data, or mobile data (depending on your location) is turned on. You should also see signal strength and another indicator in the status bar, like 3G, 4G, LTE. Also, check with your carrier to make sure that your phone is provisioned for cellular data.

If you're sure that on that iphone:

• Cellular network services are working
• Cellular (mobile) data is turned on (turned on also for each app he wants to use)
• He's not over data plan limit
• Resetting Network Settings give him no improvements
• He didn''t enable any restrictions (in ScreenTime or in Restrictions depending on the IOS version he's running)

I'm almost clueless.

Talk to his carrier

or

Have that iphone inspected at an Apple Store or Authorized Service Provider: Apple – Location Selector

Please keep us informed.

Thanks and regards

Giulio

Does that iphone have network service?

Shouldn't be this case, read this support guide, and follow ALL the steps provided:

If you see No Service or Searching on your iPhone or iPad - Apple Tugi

Did you (or your son) talk to your carrier checking his plan? What did they say?

Regards

Giulio

I see. In any case, check his data plan (if it is not unlimited).

Has he already tried to restart or force restart his device ?

Regards

Giulio

If all of the cellular settings are turned on, then he is going to have to contact the carrier for assistance.