“Your iPhone is currently unable to access cellular data or make and receive calls or messages”
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iPhone 13 Pro Max, iOS 15
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Do you have an active SIM in the phone? Looking at your screenshot, it would appear the SIM is not providing a signal. Contact your cellular carrier to see if the SIM you have is active. You can also check the steps in these support documents. If you see 'invalid SIM' or 'no SIM' on your iPhone or iPad - Apple Support and If you see No Service or Searching on your iPhone or iPad - Apple Support